diff --git a/etc/config.csh/settings b/etc/config.csh/settings
index cc9da12d65..0b5678c8c8 100644
--- a/etc/config.csh/settings
+++ b/etc/config.csh/settings
@@ -6,7 +6,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2016-2022 OpenCFD Ltd.
+#     Copyright (C) 2016-2025 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -32,7 +32,7 @@ setenv WM_COMPILER_LIB_ARCH # Ending for lib directories
 if (! $?WM_COMPILE_OPTION ) setenv WM_COMPILE_OPTION
 
 # Adjust according to system and architecture
-switch ($WM_ARCH)
+switch ("$WM_ARCH")
 case Linux:
     setenv WM_ARCH linux
 
@@ -74,11 +74,22 @@ case Linux:
     breaksw
 
 # arm64 or x86_64 architectures
+# Note: /usr/bin/{gcc,g++} normally just symlinks to clang/clang++
+# which may not behave as expected.
 case Darwin:
     setenv WM_ARCH darwin64
     if ( "$WM_COMPILER" == Gcc ) then
         setenv WM_COMPILER Clang
-        echo "openfoam (darwin): using clang instead of gcc"
+        # Honour use of gcc, when version=... is specifed in WM_COMPILE_CONTROL
+        # (eg, gcc installed via homebrew)
+        if ( $?WM_COMPILE_CONTROL ) then
+            if ( "$WM_COMPILE_CONTROL" =~ "*version=*" ) then
+                setenv WM_COMPILER Gcc
+            endif
+        endif
+        if ( "$WM_COMPILER" == Clang ) then
+            echo "openfoam (darwin): using clang instead of gcc"
+        endif
     endif
     breaksw
 
@@ -214,8 +225,8 @@ _foamEtc -config compiler
 # ThirdParty base for compilers
 set archDir="$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH"
 
-switch ("$WM_COMPILER_TYPE-$WM_COMPILER")
-case ThirdParty-Gcc*:
+switch ("${WM_COMPILER_TYPE}/${WM_COMPILER}")
+case ThirdParty/Gcc*:
     if (! $?gmp_version  ) set gmp_version=gmp-system
     if (! $?mpfr_version ) set mpfr_version=mpfr-system
     if (! $?mpc_version  ) set mpc_version=mpc-system
@@ -263,7 +274,7 @@ GCC_NOT_FOUND
     endif
     breaksw
 
-case ThirdParty-Clang*:
+case ThirdParty/Clang*:
     set clangDir="$archDir/$clang_version"
 
     # Check that the compiler directory can be found
@@ -290,9 +301,9 @@ CLANG_NOT_FOUND
     endif
     breaksw
 
-case -*:
-case system-*:
-case ThirdParty-*:
+case /*:
+case system/*:
+case ThirdParty/*:
     # Using empty (system), system compiler or other ThirdParty compiler
     breaksw
 
diff --git a/etc/config.sh/settings b/etc/config.sh/settings
index 7735c4cf41..a615345631 100644
--- a/etc/config.sh/settings
+++ b/etc/config.sh/settings
@@ -6,7 +6,7 @@
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
 #     Copyright (C) 2011-2016 OpenFOAM Foundation
-#     Copyright (C) 2016-2022 OpenCFD Ltd.
+#     Copyright (C) 2016-2025 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -70,13 +70,21 @@ Linux)
     ;;
 
 # arm64 or x86_64 architectures
+# Note: /usr/bin/{gcc,g++} normally just symlinks to clang/clang++
+# which may not behave as expected.
 Darwin)
     WM_ARCH=darwin64
-    # Defult to clang (not gcc) as system compiler
     if [ "$WM_COMPILER" = Gcc ]
     then
-        WM_COMPILER=Clang
-        echo "openfoam (darwin): using clang instead of gcc" 1>&2
+        # Honour use of gcc, when version=... is specifed in WM_COMPILE_CONTROL
+        # (eg, gcc installed via homebrew)
+        case "$WM_COMPILE_CONTROL" in
+        (*version=*) ;;
+        (*)
+            WM_COMPILER=Clang
+            echo "openfoam (darwin): using clang instead of gcc" 1>&2
+            ;;
+        esac
     fi
     ;;
 
@@ -217,8 +225,8 @@ _foamEtc -config compiler
 # ThirdParty base for compilers
 archDir="$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER_ARCH"
 
-case "$WM_COMPILER_TYPE-$WM_COMPILER" in
-ThirdParty-Gcc*)
+case "${WM_COMPILER_TYPE}/${WM_COMPILER}" in
+(ThirdParty/Gcc*)
     gccDir="$archDir/$gcc_version"
     gmpDir="$archDir/${gmp_version:-gmp-system}"
     mpfrDir="$archDir/${mpfr_version:-mpfr-system}"
@@ -259,7 +267,7 @@ GCC_NOT_FOUND
     fi
     ;;
 
-ThirdParty-Clang*)
+(ThirdParty/Clang*)
     clangDir="$archDir/$clang_version"
 
     # Check that the compiler directory can be found
@@ -285,11 +293,11 @@ CLANG_NOT_FOUND
     fi
     ;;
 
--* | system-* | ThirdParty-*)
+(/* | system/* | ThirdParty/*)
     # Using empty (system), system compiler or other ThirdParty compiler
     ;;
 
-*)
+(*)
     /bin/cat << UNKNOWN_TYPE 1>&2
 ===============================================================================
 Unknown WM_COMPILER_TYPE="$WM_COMPILER_TYPE" - treating as 'system'
diff --git a/etc/config.sh/umpire b/etc/config.sh/umpire
new file mode 100644
index 0000000000..f8db340506
--- /dev/null
+++ b/etc/config.sh/umpire
@@ -0,0 +1,30 @@
+#----------------------------------*-sh-*--------------------------------------
+# =========                 |
+# \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+#  \\    /   O peration     |
+#   \\  /    A nd           | www.openfoam.com
+#    \\/     M anipulation  |
+#------------------------------------------------------------------------------
+#     Copyright (C) 2025 OpenCFD Ltd.
+#------------------------------------------------------------------------------
+# License
+#     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
+#
+# File
+#     etc/config.sh/umpire
+#     [experimental]
+#
+# Description
+#     Setup for UMPIRE include/libraries (usually ThirdParty installation).
+#
+# Note
+#     No csh version. This file is only used by wmake.
+#
+#------------------------------------------------------------------------------
+# USER EDITABLE PART: Changes made here may be lost with the next upgrade
+
+umpire_version=umpire-2025.03.0
+export UMPIRE_ARCH_PATH="$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER/$umpire_version"
+
+# END OF (NORMAL) USER EDITABLE PART
+#------------------------------------------------------------------------------
diff --git a/src/OSspecific/POSIX/Allwmake b/src/OSspecific/POSIX/Allwmake
index 0da34ed520..7bc223e001 100755
--- a/src/OSspecific/POSIX/Allwmake
+++ b/src/OSspecific/POSIX/Allwmake
@@ -4,12 +4,58 @@ targetType=libo                                     # Preferred library type
 . ${WM_PROJECT_DIR:?}/wmake/scripts/AllwmakeParseArguments $*
 
 #------------------------------------------------------------------------------
+# Hack for MacOS (with Gcc).
+# The gcc compiler include path has something like this:
+#     /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include
+#
+# but xcode flex installs under this:
+#     /Applications/Xcode.app/Contents/Developer/
+#      Toolchains/XcodeDefault.xctoolchain/usr/include
+
+case "${WM_ARCH}/${WM_COMPILER}" in
+(darwin*/Gcc*)
+    if [ ! -f FlexLexer.h ]
+    then
+        # Remove stale link(s)
+        rm -f FlexLexer.h lnInclude/FlexLexer.h
+
+        for include in \
+            /usr/include \
+            /Library/Developer/CommandLineTools/SDKs/MacOSX15.sdk/usr/include \
+            /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include \
+        ;
+        do
+            if [ -f "$include"/FlexLexer.h ]
+            then
+                echo "Adding FlexLexer.h link to ${PWD##*/} (darwin/gcc)" 1>&2
+                ln -sf "$include"/FlexLexer.h FlexLexer.h
+
+                if [ -d lnInclude ]
+                then
+                    (cd lnInclude && ln -sf ../FlexLexer.h .)
+                fi
+                break
+            fi
+        done
+    fi
+    ;;
+(*)
+    if [ -f FlexLexer.h ]
+    then
+        echo "Removing old FlexLexer.h link from ${PWD##*/}" 1>&2
+        rm -f FlexLexer.h lnInclude/FlexLexer.h
+    fi
+    ;;
+esac
+
+#------------------------------------------------------------------------------
+
 unset COMP_FLAGS LINK_FLAGS
 
 # If <sys/inotify.h> is available (Linux)
 if [ -f /usr/include/sys/inotify.h ]
 then
-    echo "    found <sys/inotify.h>  --  enabling inotify for file monitoring."
+    echo "    found <sys/inotify.h> -- using inotify for file monitoring" 1>&2
     export COMP_FLAGS="-DFOAM_USE_INOTIFY"
 fi
 
diff --git a/wmake/rules/darwin64/link-c b/wmake/rules/darwin64/link-c
new file mode 100644
index 0000000000..efaeba873f
--- /dev/null
+++ b/wmake/rules/darwin64/link-c
@@ -0,0 +1,11 @@
+#------------------------------------------------------------------------------
+# Linking on MacOS - without rpath components
+#------------------------------------------------------------------------------
+
+LINK_LIBS   = $(cDBUG)
+
+LINKLIBSO   = $(cc) $(cARCH) -Wl,-dylib,-undefined,dynamic_lookup
+
+LINKEXE     = $(cc) $(cARCH) -Wl,-execute,-undefined,dynamic_lookup
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64/link-c++ b/wmake/rules/darwin64/link-c++
new file mode 100644
index 0000000000..9a3eccfc99
--- /dev/null
+++ b/wmake/rules/darwin64/link-c++
@@ -0,0 +1,13 @@
+#------------------------------------------------------------------------------
+# Linking on MacOS
+# with or without rpath components
+# - current default is with rpath unless explicitly disabled
+#------------------------------------------------------------------------------
+
+ifneq (,$(findstring ~rpath,$(WM_COMPILE_CONTROL)))
+    include $(ARCHITECTURE_RULES)/link-no-c++
+else
+    include $(ARCHITECTURE_RULES)/link-rpath-c++
+endif
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64/link-no-path-c++ b/wmake/rules/darwin64/link-no-path-c++
new file mode 100644
index 0000000000..02d418e941
--- /dev/null
+++ b/wmake/rules/darwin64/link-no-path-c++
@@ -0,0 +1,13 @@
+#------------------------------------------------------------------------------
+# Linking on MacOS - without rpath components
+#------------------------------------------------------------------------------
+
+LINK_LIBS   = $(c++DBUG)
+
+LINKLIBSO   = $(CC) $(c++FLAGS) \
+    -Wl,-dylib,-undefined,dynamic_lookup
+
+LINKEXE     = $(CC) $(c++FLAGS) \
+    -Wl,-execute,-undefined,dynamic_lookup
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Clang/link-rpath-c++ b/wmake/rules/darwin64/link-rpath-c++
similarity index 75%
rename from wmake/rules/darwin64Clang/link-rpath-c++
rename to wmake/rules/darwin64/link-rpath-c++
index f7a7cd6001..9fa0c6aa5b 100644
--- a/wmake/rules/darwin64Clang/link-rpath-c++
+++ b/wmake/rules/darwin64/link-rpath-c++
@@ -1,5 +1,8 @@
 #------------------------------------------------------------------------------
-include $(DEFAULT_RULES)/rpath
+# Linking on MacOS - with rpath components
+#------------------------------------------------------------------------------
+
+include $(ARCHITECTURE_RULES)/rpath
 
 LINK_LIBS   = $(c++DBUG)
 
diff --git a/wmake/rules/darwin64Clang/rpath b/wmake/rules/darwin64/rpath
similarity index 88%
rename from wmake/rules/darwin64Clang/rpath
rename to wmake/rules/darwin64/rpath
index 834b8f1693..e6d61e0408 100644
--- a/wmake/rules/darwin64Clang/rpath
+++ b/wmake/rules/darwin64/rpath
@@ -1,4 +1,6 @@
 #------------------------------------------------------------------------------
+# Linking with rpath components (MacOS)
+#------------------------------------------------------------------------------
 
 # Compile-time rpath information:
 
diff --git a/wmake/rules/darwin64Clang/c b/wmake/rules/darwin64Clang/c
index 3083b281ed..0ad4dc8a37 100644
--- a/wmake/rules/darwin64Clang/c
+++ b/wmake/rules/darwin64Clang/c
@@ -17,10 +17,7 @@ cFLAGS      = \
 
 ctoo        = $(WM_SCHEDULER) $(cc) $(cFLAGS) -c $< -o $@
 
-LINK_LIBS   = $(cDBUG)
-
-LINKLIBSO   = $(cc) $(cARCH) -Wl,-dylib,-undefined,dynamic_lookup
-
-LINKEXE     = $(cc) $(cARCH) -Wl,-execute,-undefined,dynamic_lookup
+# MacOS linking
+include $(ARCHITECTURE_RULES)/link-c
 
 #------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Clang/c++ b/wmake/rules/darwin64Clang/c++
index 7793657344..746b3fe7b3 100644
--- a/wmake/rules/darwin64Clang/c++
+++ b/wmake/rules/darwin64Clang/c++
@@ -21,15 +21,7 @@ cpptoo      = $(Ctoo)
 cxxtoo      = $(Ctoo)
 
 
-# Linking:
-# with or without rpath components on MacOS
-# - current default is with rpath unless explicitly disabled
-
-ifneq (,$(findstring ~rpath,$(WM_COMPILE_CONTROL)))
-    include $(DEFAULT_RULES)/link-c++
-
-else
-    include $(DEFAULT_RULES)/link-rpath-c++
-endif
+# MacOS linking (with or without rpath components)
+include $(ARCHITECTURE_RULES)/link-c++
 
 #------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Clang/link-c++ b/wmake/rules/darwin64Clang/link-c++
deleted file mode 100644
index d1c1f6e6a7..0000000000
--- a/wmake/rules/darwin64Clang/link-c++
+++ /dev/null
@@ -1,9 +0,0 @@
-#------------------------------------------------------------------------------
-
-LINK_LIBS   = $(c++DBUG)
-
-LINKLIBSO   = $(CC) $(c++FLAGS) -Wl,-dylib,-undefined,dynamic_lookup
-
-LINKEXE     = $(CC) $(c++FLAGS) -Wl,-execute,-undefined,dynamic_lookup
-
-#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Gcc/c b/wmake/rules/darwin64Gcc/c
new file mode 100644
index 0000000000..cf3924bb6c
--- /dev/null
+++ b/wmake/rules/darwin64Gcc/c
@@ -0,0 +1,23 @@
+#------------------------------------------------------------------------------
+include $(GENERAL_RULES)/Gcc/c
+
+## ifneq (,$(findstring +xcrun,$(WM_COMPILE_CONTROL)))
+## cc         := xcrun cc
+## endif
+
+cARCH      := -m64 -ftrapping-math
+
+ifneq (,$(strip $(WM_COMPILE_OPTION)))
+    sinclude $(DEFAULT_RULES)/c$(WM_COMPILE_OPTION)
+endif
+
+cFLAGS      = \
+    $(cARCH) $(GFLAGS) $(cWARN) $(cOPT) $(cDBUG) \
+    $(FOAM_EXTRA_CFLAGS) $(LIB_HEADER_DIRS) -fPIC
+
+ctoo        = $(WM_SCHEDULER) $(cc) $(cFLAGS) -c $< -o $@
+
+# MacOS linking
+include $(ARCHITECTURE_RULES)/link-c
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Gcc/c++ b/wmake/rules/darwin64Gcc/c++
new file mode 100644
index 0000000000..e10fcaa713
--- /dev/null
+++ b/wmake/rules/darwin64Gcc/c++
@@ -0,0 +1,27 @@
+#------------------------------------------------------------------------------
+include $(GENERAL_RULES)/Gcc/c++
+
+## ifneq (,$(findstring +xcrun,$(WM_COMPILE_CONTROL)))
+## CC         := xcrun c++ -std=c++17
+## endif
+
+c++ARCH    := -m64 -pthread -ftrapping-math
+
+ifneq (,$(strip $(WM_COMPILE_OPTION)))
+    sinclude $(DEFAULT_RULES)/c++$(WM_COMPILE_OPTION)
+endif
+
+c++FLAGS    = \
+    $(c++ARCH) $(GFLAGS) $(c++WARN) $(c++OPT) $(c++DBUG) $(ptFLAGS) \
+    $(FOAM_EXTRA_CXXFLAGS) $(LIB_HEADER_DIRS) -fPIC
+
+Ctoo        = $(WM_SCHEDULER) $(CC) $(c++FLAGS) -c $< -o $@
+cctoo       = $(Ctoo)
+cpptoo      = $(Ctoo)
+cxxtoo      = $(Ctoo)
+
+
+# MacOS linking (with or without rpath components)
+include $(ARCHITECTURE_RULES)/link-c++
+
+#------------------------------------------------------------------------------
diff --git a/wmake/rules/darwin64Gcc/general b/wmake/rules/darwin64Gcc/general
new file mode 100644
index 0000000000..64c1945a66
--- /dev/null
+++ b/wmake/rules/darwin64Gcc/general
@@ -0,0 +1,16 @@
+CPP        = cpp -traditional-cpp $(GFLAGS)
+
+include $(GENERAL_RULES)/standard
+include $(GENERAL_RULES)/Gcc/openmp
+
+ifneq (,$(findstring ~openmp,$(WM_COMPILE_CONTROL)))
+    include $(GENERAL_RULES)/no-openmp
+endif
+
+include $(DEFAULT_RULES)/c
+include $(DEFAULT_RULES)/c++
+
+# Shared library extension (with '.' separator)
+EXT_SO  = .dylib
+
+# -----------------------------------------------------------------------------
diff --git a/wmake/scripts/have_umpire b/wmake/scripts/have_umpire
new file mode 100644
index 0000000000..46991e678b
--- /dev/null
+++ b/wmake/scripts/have_umpire
@@ -0,0 +1,169 @@
+#----------------------------------*-sh-*--------------------------------------
+# =========                 |
+# \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+#  \\    /   O peration     |
+#   \\  /    A nd           | www.openfoam.com
+#    \\/     M anipulation  |
+#------------------------------------------------------------------------------
+#     Copyright (C) 2025 OpenCFD Ltd.
+#------------------------------------------------------------------------------
+# License
+#     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
+#
+# Script
+#     have_umpire
+#
+# Description
+#     Detection/setup of UMPIRE
+#
+# Requires
+#     UMPIRE_ARCH_PATH
+#
+# Functions provided
+#     have_umpire, no_umpire, echo_umpire, query_umpire, search_umpire
+#
+# Variables set on success
+#     HAVE_UMPIRE
+#     UMPIRE_ARCH_PATH
+#     UMPIRE_INC_DIR
+#     UMPIRE_LIB_DIR
+#
+#------------------------------------------------------------------------------
+. ${WM_PROJECT_DIR:?}/wmake/scripts/sysFunctions    # General system functions
+
+#------------------------------------------------------------------------------
+
+# Reset
+no_umpire()
+{
+    unset HAVE_UMPIRE UMPIRE_INC_DIR UMPIRE_LIB_DIR
+}
+
+
+# Report
+echo_umpire()
+{
+    echo "umpire=${HAVE_UMPIRE:-false}"
+    echo "root=\"$UMPIRE_ARCH_PATH\""
+    echo "include=\"$UMPIRE_INC_DIR\""
+    echo "library=\"$UMPIRE_LIB_DIR\""
+}
+
+
+# Search
+# $1 : prefix (*_ARCH_PATH, system, ...)
+#
+# On success, return 0 and export variables
+# -> HAVE_UMPIRE, UMPIRE_INC_DIR, UMPIRE_LIB_DIR
+search_umpire()
+{
+    local warn # warn="==> skip umpire"
+    local incName="Umpire.hpp"
+    local libName="libumpire"
+
+    local prefix="${1:-system}"
+    local header library
+
+    # ----------------------------------
+    if isNone "$prefix"
+    then
+        [ -n "$warn" ] && echo "$warn (disabled)"
+        return 1
+    elif hasAbsdir "$prefix"
+    then
+        header=$(findFirstFile "$prefix/include/umpire/$incName")
+        library=$(findExtLib "$libName")
+    elif isSystem "$prefix"
+    then
+        header=$(findFirstFile \
+            "/usr/local/include/umpire/$incName" \
+            "/usr/include/umpire/$incName" \
+        )
+        prefix=$(sysPrefix "$header")
+    else
+        unset prefix
+    fi
+    # ----------------------------------
+
+    # Header
+    [ -n "$header" ] || {
+        [ -n "$warn" ] && echo "$warn (no header)"
+        return 2
+    }
+
+    # Library
+    [ -n "$library" ] \
+    || library=$(findLibrary -prefix="$prefix" -name="$libName") \
+    || {
+        [ -n "$warn" ] && echo "$warn (no library)"
+        return 2
+    }
+
+    # ----------------------------------
+
+    # OK
+    export HAVE_UMPIRE=true
+    export UMPIRE_ARCH_PATH="$prefix"
+    export UMPIRE_INC_DIR="${header%/*}"     # Basename
+    export UMPIRE_LIB_DIR="${library%/*}"    # Basename
+
+    # Expect path/include/umpire -> path/include
+    UMPIRE_INC_DIR="${UMPIRE_INC_DIR%/umpire}"
+}
+
+
+# Output as per search_* function
+have_umpire()
+{
+    local warn # warn="==> skip umpire"
+    local config="config.sh/umpire"
+    local file
+
+    if file="$("$WM_PROJECT_DIR"/bin/foamEtcFile "$config")"
+    then
+        . "$file"
+    else
+        [ -n "$warn" ] && echo "$warn (no $config)"
+        return 2
+    fi
+
+    search_umpire "$UMPIRE_ARCH_PATH"
+}
+
+
+# Query settings
+query_umpire()
+{
+    local config="config.sh/umpire"
+    local file
+
+    if file="$("$WM_PROJECT_DIR"/bin/foamEtcFile -mode=o "$config")"
+    then
+        . "$file"
+        _process_query umpire "$UMPIRE_ARCH_PATH"
+    else
+        echo "(no $config)" 1>&2
+        echo "umpire=unknown"
+    fi
+}
+
+
+#------------------------------------------------------------------------------
+
+# Reset
+no_umpire
+
+# Test/query
+case "$1" in
+-test | -debug-test)
+    [ "$1" = "-debug-test" ] && set -x
+    have_umpire
+    [ "$1" = "-debug-test" ] && set +x
+    echo_umpire
+    ;;
+-query)
+    query_umpire
+    ;;
+esac
+
+#------------------------------------------------------------------------------