diff --git a/BUILD b/BUILD
index c73e2c1..d7bab2d 100644
--- a/BUILD
+++ b/BUILD
@@ -18,10 +18,3 @@ Include('web')
 Include('pico-ice')
 Include('esp32')
 Include('site')
-
-Default('windows')
-Default('posix')
-Default('web')
-Default('esp32')
-Default('pico')
-Default('site')
diff --git a/configure.py b/configure.py
index 87e39a9..1b845df 100755
--- a/configure.py
+++ b/configure.py
@@ -26,6 +26,14 @@ SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
 ROOT_DIR = SCRIPT_DIR
 NINJA_BUILD = os.path.join(ROOT_DIR, 'build.ninja')
 
+SRC_DIR = os.path.relpath(ROOT_DIR, os.getcwd())
+if SRC_DIR == '.':
+  DST_DIR = 'out'
+  NINJA_DIR = '.'
+else:
+  DST_DIR = '.'
+  NINJA_DIR = '.'
+
 CFLAGS_COMMON = [
   '-O2',
   '-I', '$src',
@@ -105,42 +113,85 @@ WIN_LFLAGS64 = [
   '/LIBPATH:"c:/Program Files (x86)/Windows Kits/10/Lib/10.0.19041.0/ucrt/x64"',
 ] + WIN_LIBS
 
-LOCALAPPDATAR = str(subprocess.check_output('cmd.exe /c echo "%LOCALAPPDATA%"',
-                                            shell=True, stderr=subprocess.DEVNULL).splitlines()[0], 'ascii').replace('\\', '/')
-LOCALAPPDATA = LOCALAPPDATAR.replace('C:/', '/mnt/c/')
-ARDUINO_CLI = LOCALAPPDATA + '/Programs/arduino-ide/resources/app/lib/backend/resources/arduino-cli.exe'
-WINTMP = LOCALAPPDATA + '/Temp'
-WINTMPR = LOCALAPPDATAR + '/Temp'
+PICO_ICE_ENABLED = False
+WINDOWS_ENABLED = False
+
+WINTMP = '/UNSUPPORTED'
+ARDUINO_CLI = 'UNSUPPORTED'
+WIN_CL32 = 'UNSUPPORTED'
+WIN_CL64 = 'UNSUPPORTED'
+WIN_LINK32 = 'UNSUPPORTED'
+WIN_LINK64 = 'UNSUPPORTED'
+WIN_RC32 = 'UNSUPPORTED'
+WIN_RC64 = 'UNSUPPORTED'
+
+# Mutable global state.
+build_files = []
+output = ''
 
 def Escape(path):
   return path.replace(' ', '\\ ').replace('(', '\\(').replace(')', '\\)')
 
 def LSQ(path):
-  return '"' + str(subprocess.check_output('ls ' + Escape(path), shell=True), 'ascii').splitlines()[0] + '"'
+  return '"' + str(subprocess.check_output('ls ' + Escape(path), shell=True,
+                                           stderr=subprocess.DEVNULL), 'ascii').splitlines()[0] + '"'
 
-PROGFILES = '/mnt/c/Program Files (x86)'
-MSVS = PROGFILES + '/Microsoft Visual Studio'
-MSKITS = PROGFILES + '/Windows Kits'
-WIN_CL32 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x86/cl.exe')
-WIN_CL64 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x64/cl.exe')
-WIN_LINK32 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x86/link.exe')
-WIN_LINK64 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x64/link.exe')
-WIN_RC32 = LSQ(MSKITS + '/*/bin/*/x86/rc.exe')
-WIN_RC64 = LSQ(MSKITS + '/*/bin/*/x64/rc.exe')
+def DetectWindowsTools(args):
+  global WINDOWS_ENABLED
+  global WINTMP, ARDUINO_CLI
+  global WIN_CL32, WIN_CL64, WIN_LINK32, WIN_LINK64, WIN_RC32, WIN_RC64
+  try:
+    LOCALAPPDATAR = str(subprocess.check_output('cmd.exe /c echo "%LOCALAPPDATA%"', shell=True,
+                                                stderr=subprocess.DEVNULL).splitlines()[0], 'ascii').replace('\\', '/')
+  except:
+    if not args.quiet:
+      sys.stderr.write('Windows %LOCALAPPDATA% not available, Windows support disabled.\n')
+    return
+  LOCALAPPDATA = LOCALAPPDATAR.replace('C:/', '/mnt/c/')
+  ARDUINO_CLI = LOCALAPPDATA + '/Programs/arduino-ide/resources/app/lib/backend/resources/arduino-cli.exe'
+  WINTMP = LOCALAPPDATA + '/Temp'
+  WINTMPR = LOCALAPPDATAR + '/Temp'
+  PROGFILES = '/mnt/c/Program Files (x86)'
+  MSVS = PROGFILES + '/Microsoft Visual Studio'
+  MSKITS = PROGFILES + '/Windows Kits'
+  try:
+    WIN_CL32 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x86/cl.exe')
+    WIN_CL64 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x64/cl.exe')
+    WIN_LINK32 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x86/link.exe')
+    WIN_LINK64 = LSQ(MSVS + '/*/*/VC/Tools/MSVC/*/bin/Hostx86/x64/link.exe')
+    WIN_RC32 = LSQ(MSKITS + '/*/bin/*/x86/rc.exe')
+    WIN_RC64 = LSQ(MSKITS + '/*/bin/*/x64/rc.exe')
+  except:
+    if not args.quiet:
+      sys.stderr.write('Windows tools not available, Windows support disabled.\n')
+    return
+  WINDOWS_ENABLED = True
 
-D8 = LSQ('${HOME}/src/v8/v8/out/x64.release/d8')
-NODEJS = LSQ('/usr/bin/nodejs')
 
-SRC_DIR = os.path.relpath(ROOT_DIR, os.getcwd())
-if SRC_DIR == '.':
-  DST_DIR = 'out'
-  NINJA_DIR = '.'
-else:
-  DST_DIR = '.'
-  NINJA_DIR = '.'
+def DetectGenericTools(args):
+  global D8, NODEJS, PICO_ICE_ENABLED
+  try:
+    D8 = LSQ('${HOME}/src/v8/v8/out/x64.release/d8')
+  except:
+    if not args.quiet:
+      sys.stderr.write('V8 checkout in $HOME/src/v8 not found, ignoring.\n')
+  try:
+    NODEJS = LSQ('/usr/bin/nodejs')
+  except:
+    if not args.quiet:
+      sys.stderr.write('/usr/bin/nodejs not found, required!\n')
+      sys.exit(1)
+  try:
+    LSQ('/usr/bin/arm-none-eabi-gcc')
+    PICO_ICE_ENABLED = True
+  except:
+    if not args.quiet:
+      sys.stderr.write('Missing package gcc-arm-none-eabi, pico-ice diabled!\n')
 
-build_files = []
-output = f"""
+
+def InitOutput():
+  global output
+  output = f"""
 ninja_required_version = 1.1
 src = {SRC_DIR}
 dst = {DST_DIR}
@@ -456,11 +507,22 @@ def Default(target):
   return target
 
 
+class SkipFileException(Exception):
+  pass
+
+
+def Return():
+  raise SkipFileException()
+
+
 def Include(path):
   build_files.append(os.path.join('$src', path, 'BUILD'))
   path = os.path.join(ROOT_DIR, path, 'BUILD')
   data = open(path).read()
-  exec(data)
+  try:
+    exec(data)
+  except SkipFileException:
+    pass
 
 
 def Main():
@@ -469,6 +531,9 @@ def Main():
     description='Generate ninja.build')
   parser.add_argument('-q', '--quiet', action='store_true')
   args = parser.parse_args()
+  DetectGenericTools(args)
+  DetectWindowsTools(args)
+  InitOutput()
   Include('.')
   with open('build.ninja', 'w') as fh:
     fh.write(output)
diff --git a/esp32/BUILD b/esp32/BUILD
index 022d254..b79b4a8 100644
--- a/esp32/BUILD
+++ b/esp32/BUILD
@@ -66,6 +66,7 @@ Run('$dst/gen/esp32_sim_opcodes.h', '$dst/gen/print-esp32-builtins')
 
 # Main Alias.
 Alias('esp32', ' '.join(ESP32_FILES))
+Default('esp32')
 
 # Automate building / flashing.
 BOARDS = {
diff --git a/pico-ice/BUILD b/pico-ice/BUILD
index 52c56dc..7352628 100644
--- a/pico-ice/BUILD
+++ b/pico-ice/BUILD
@@ -12,6 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+if not PICO_ICE_ENABLED:
+  Return()
+
 PICO_ICE_FILES = []
 PICO_ICE_ZIP_FILES = []
 
@@ -42,12 +45,18 @@ Command(' '.join(['$dst/pico-ice/build.ninja',
         'cmake $dst/pico-ice -G Ninja -S pico-ice -B $dst/pico-ice 2>&1 | cat >$dst/pico-ice/cmake.err')
 
 # Check out submodules if needed.
-Command('$src/pico-ice/pico-sdk/README.md',
+Command(' '.join([
+          '$src/pico-ice/pico-sdk/README.md',
+          '$src/pico-ice/pico-sdk/LICENSE.TXT',
+        ]),
         '', 'git submodule update --init pico-ice/pico-sdk')
 Command('$src/pico-ice/pico-sdk/lib/tinyusb/README.rst',
         '$src/pico-ice/pico-sdk/README.md',
 	      'cd $src/pico-ice/pico-sdk && git submodule update --init lib/tinyusb')
-Command('pico-ice/pico-ice-sdk/README.md',
+Command(' '.join([
+          '$src/pico-ice/pico-ice-sdk/README.md',
+          '$src/pico-ice/pico-ice-sdk/LICENSE.md',
+        ]),
 	      '', 'git submodule update --init pico-ice/pico-ice-sdk')
 
 # Zip it.
@@ -65,3 +74,4 @@ Importation('$dst/gen/pico_ice_boot.h', '$src/pico-ice/pico_ice_boot.fs', name='
 
 # Main Alias.
 Alias('pico', ' '.join(PICO_ICE_FILES))
+Default('pico')
diff --git a/posix/BUILD b/posix/BUILD
index b4ffa1e..ac1c8a3 100644
--- a/posix/BUILD
+++ b/posix/BUILD
@@ -25,3 +25,5 @@ OneShot('install',
         '$dst/posix/ueforth',
         'sudo cp $dst/posix/ueforth /usr/bin/ueforth',
         pool='console')
+
+Default('posix')
diff --git a/site/BUILD b/site/BUILD
index 7ce0940..002f127 100644
--- a/site/BUILD
+++ b/site/BUILD
@@ -48,11 +48,15 @@ DEPLOY_ITEMS += [
     'esp-cam-wiring.jpg',
     'serial_bridge.jpg',
   ]
-] + [
-  Copy('$dst/deploy/static/favicon.ico', '$dst/resources/eforth.ico'),
 ]
 
+if WINDOWS_ENABLED:
+  DEPLOY_ITEM += [
+    Copy('$dst/deploy/static/favicon.ico', '$dst/resources/eforth.ico'),
+  ]
+
 Alias('site', ' '.join(DEPLOY_ITEMS))
+Default('site')
 
 Alias('deploy', ' '.join([
   Command('deploy-esp32', 'site',
@@ -61,7 +65,9 @@ Alias('deploy', ' '.join([
 	        'cd $dst/deploy && gcloud app deploy -q --project eforth *.yaml', pool='console'),
 ]))
 
-PUBLISH_PARTS = [
+PUBLISH_PARTS = []
+
+PUBLISH_PARTS += [
   Alias('publish-esp32', ' '.join([
     Publish('publish-esp32-rev',
            '$dst/esp32/ESP32forth.zip',
@@ -70,14 +76,6 @@ PUBLISH_PARTS = [
              '$dst/esp32/ESP32forth.zip',
              'ESP32forth-{{VERSION}}.zip'),
   ])),
-  Alias('publish-pico-ice', ' '.join([
-    Publish('publish-pico-ice-rev',
-             '$dst/pico-ice/ueforth-pico-ice.zip',
-             'ueforth-pico-ice-{{VERSION}}-{{REVSHORT}}.zip'),
-    Publish('publish-pico-ice-ver',
-             '$dst/pico-ice/ueforth-pico-ice.zip',
-             'ueforth-pico-ice-{{VERSION}}.zip'),
-  ])),
   Alias('publish-linux', ' '.join([
     Publish('publish-linux-rev',
              '$dst/posix/ueforth',
@@ -94,26 +92,42 @@ PUBLISH_PARTS = [
              '$dst/web/ueforth.js',
              'ueforth-{{VERSION}}.js'),
   ])),
-  Alias('publish-win', ' '.join([
-    Alias('publish-win32', ' '.join([
-      Publish('publish-win32-rev',
-               '$dst/windows/uEf32.exe',
-               'uEf32-{{VERSION}}-{{REVSHORT}}.exe'),
-      Publish('publish-win32-ver',
-               '$dst/windows/uEf32.exe',
-               'uEf32-{{VERSION}}.exe'),
-    ])),
-    Alias('publish-win64', ' '.join([
-      Publish('publish-win64-rev',
-               '$dst/windows/uEf64.exe',
-               'uEf64-{{VERSION}}-{{REVSHORT}}.exe'),
-      Publish('publish-win64-ver',
-               '$dst/windows/uEf64.exe',
-               'uEf64-{{VERSION}}.exe'),
-    ])),
-  ])),
 ]
 
+if PICO_ICE_ENABLED:
+  PUBLISH_PARTS += [
+    Alias('publish-pico-ice', ' '.join([
+      Publish('publish-pico-ice-rev',
+               '$dst/pico-ice/ueforth-pico-ice.zip',
+               'ueforth-pico-ice-{{VERSION}}-{{REVSHORT}}.zip'),
+      Publish('publish-pico-ice-ver',
+               '$dst/pico-ice/ueforth-pico-ice.zip',
+               'ueforth-pico-ice-{{VERSION}}.zip'),
+    ])),
+  ]
+
+if WINDOWS_ENABLED:
+  PUBLISH_PARTS += [
+    Alias('publish-win', ' '.join([
+      Alias('publish-win32', ' '.join([
+        Publish('publish-win32-rev',
+                 '$dst/windows/uEf32.exe',
+                 'uEf32-{{VERSION}}-{{REVSHORT}}.exe'),
+        Publish('publish-win32-ver',
+                 '$dst/windows/uEf32.exe',
+                 'uEf32-{{VERSION}}.exe'),
+      ])),
+      Alias('publish-win64', ' '.join([
+        Publish('publish-win64-rev',
+                 '$dst/windows/uEf64.exe',
+                 'uEf64-{{VERSION}}-{{REVSHORT}}.exe'),
+        Publish('publish-win64-ver',
+                 '$dst/windows/uEf64.exe',
+                 'uEf64-{{VERSION}}.exe'),
+      ])),
+    ])),
+  ]
+
 Alias('publish', ' '.join([
   Command('publish-index', ' '.join([
       '$src/tools/webindex.py',
diff --git a/web/BUILD b/web/BUILD
index 1fb34fb..6f92b30 100644
--- a/web/BUILD
+++ b/web/BUILD
@@ -34,3 +34,4 @@ WEB_ITEMS = [
 ]
 
 Alias('web', ' '.join(WEB_ITEMS))
+Default('web')
diff --git a/windows/BUILD b/windows/BUILD
index 3294ebe..de722a9 100644
--- a/windows/BUILD
+++ b/windows/BUILD
@@ -12,7 +12,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+if not WINDOWS_ENABLED:
+  Return()
+
 Alias('windows', 'win32 win64')
+Default('windows')
 
 # Create boot.
 Importation('$dst/gen/windows_boot.h', '$src/windows/windows_boot.fs',