diff --git a/demo/gnucompat-demo.sh b/demo/gnucompat-demo.sh
index 90f13f6..79ffe6f 100755
--- a/demo/gnucompat-demo.sh
+++ b/demo/gnucompat-demo.sh
@@ -8,6 +8,16 @@ declare -r SCRIPT_DIR
 # shellcheck source=/dev/null
 source "${SCRIPT_DIR}/../lib_gnucompat.sh"
 
+# ASSUME_GNU:
+#
+# Set to "no" to assume non-GNU tools. Defaults to "yes".
+# This flag is especially meant to be used in the CI to test with different
+# environments set up by the CI. Note, that this does not trigger an enforced
+# check of Non-GNU tools, it just triggers a more defensive execution. This is,
+# because the CI might have GNU tools installed by default, but the script
+# should still be able to run successfully.
+readonly ASSUME_GNU="${ASSUME_GNU:-yes}"
+
 # Function to output the path and GNU status of a command
 function output_command_info() {
   local cmd_var_name="${1}"
@@ -39,3 +49,251 @@ output_command_info "TR"
 output_command_info "UNIQ"
 output_command_info "WC"
 output_command_info "DIFF"
+
+# ------------------------------------------------------------------------------
+# Demo for GNU/Non-GNU Compatibility Layer
+#
+# If ASSUME_GNU is set to "yes", the script will run as if all tools are GNU
+# tools. If set to "no", the script will run as if all tools are non-GNU tools.
+#
+# Thus, if you set to "yes", but the script execution will fail, it may be a
+# proof that the demoed library `lib_gnucompat.sh` is not working correctly.
+# ------------------------------------------------------------------------------
+
+function demo_sed() {
+  echo "SED Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    local -r sed_script='s/World/GNU/g'
+    # This command will fail if the GNU version of `sed` is not available.
+    echo "${input}" | "${SED}" --regexp-extended "${sed_script}"
+    ;;
+  *)
+    local -r sed_script='s/World/Non-GNU/g'
+    echo "${input}" | "${SED}" -r "${sed_script}"
+    ;;
+  esac
+}
+
+function demo_awk() {
+  echo "AWK Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # shellcheck disable=SC2016
+    local -r awk_script='{ print "Hello, GNU!" }'
+    # This command will fail if the GNU version of `sed` is not available.
+    echo "${input}" | "${AWK}" --non-decimal-data "${awk_script}"
+    ;;
+  *)
+    # shellcheck disable=SC2016
+    local -r awk_script='{ print "Hello, Non-GNU!" }'
+    echo "${input}" | "${AWK}" "${awk_script}"
+    ;;
+  esac
+}
+
+function demo_grep() {
+  echo "GREP Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    local -r grep_pattern="World"
+    # This command will fail if the GNU version of `grep` is not available.
+    echo "${input}" | "${GREP}" --only-matching "${grep_pattern}"
+    ;;
+  *)
+    local -r grep_pattern="World"
+    echo "${input}" | "${GREP}" "${grep_pattern}"
+    ;;
+  esac
+}
+
+function demo_sort() {
+  echo "SORT Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `sort` is not available.
+    echo "${input}" | "${SORT}" --ignore-leading-blanks
+    ;;
+  *)
+    echo "${input}" | "${SORT}"
+    ;;
+  esac
+}
+
+function demo_date() {
+  echo "DATE Demo:"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `date` is not available.
+    "${DATE}" --utc
+    ;;
+  *)
+    "${DATE}"
+    ;;
+  esac
+}
+
+function demo_xargs() {
+  echo "XARGS Demo:"
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `xargs` is not available.
+    echo "${input}" | "${XARGS}" --no-run-if-empty echo
+    ;;
+  *)
+    echo "${input}" | "${XARGS}" echo
+    ;;
+  esac
+}
+
+function demo_cut() {
+  echo "CUT Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `cut` is not available.
+    echo "${input}" | "${CUT}" --characters=3
+    ;;
+  *)
+    echo "${input}" | "${CUT}" -c 3
+    ;;
+  esac
+}
+
+function demo_head() {
+  echo "HEAD Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `head` is not available.
+    echo "${input}" | "${HEAD}" --lines=1
+    ;;
+  *)
+    echo "${input}" | "${HEAD}" -n 1
+    ;;
+  esac
+}
+
+function demo_tail() {
+  echo "TAIL Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `tail` is not available.
+    echo "${input}" | "${TAIL}" --lines=1
+    ;;
+  *)
+    echo "${input}" | "${TAIL}" -n 1
+    ;;
+  esac
+}
+
+function demo_tr() {
+  echo "TR Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `tr` is not available.
+    echo "${input}" | "${TR}" --delete ' '
+    ;;
+  *)
+    echo "${input}" | "${TR}" -d ' '
+    ;;
+  esac
+}
+
+function demo_uniq() {
+  echo "UNIQ Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `uniq` is not available.
+    echo "${input}" | "${UNIQ}" --count
+    ;;
+  *)
+    echo "${input}" | "${UNIQ}" -c
+    ;;
+  esac
+}
+
+function demo_wc() {
+  echo "WC Demo:"
+
+  local -r input="  Hello, World!"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `wc` is not available.
+    echo "${input}" | "${WC}" --words
+    ;;
+  *)
+    echo "${input}" | "${WC}" -w
+    ;;
+  esac
+}
+
+function demo_diff() {
+  echo "DIFF Demo:"
+
+  local -r input1="Hello, World!"
+  local -r input2="Hello, Universe!"
+  local -r file1="/tmp/file1.txt"
+  local -r file2="/tmp/file2.txt"
+
+  echo "${input1}" >"${file1}"
+  echo "${input2}" >"${file2}"
+
+  case "${ASSUME_GNU}" in
+  yes)
+    # This command will fail if the GNU version of `diff` is not available.
+    "${DIFF}" --brief "${file1}" "${file2}"
+    ;;
+  *)
+    "${DIFF}" "${file1}" "${file2}"
+    ;;
+  esac
+}
+
+function demo_all() {
+  demo_sed
+  demo_awk
+  demo_grep
+  demo_sort
+  demo_date
+  demo_xargs
+  demo_cut
+  demo_head
+  demo_tail
+  demo_tr
+  demo_uniq
+  demo_wc
+  demo_diff
+}
+
+# Run all demos
+demo_all
diff --git a/demo/system-tests-demo.yml b/demo/system-tests-demo.yml
new file mode 100644
index 0000000..a179c52
--- /dev/null
+++ b/demo/system-tests-demo.yml
@@ -0,0 +1,33 @@
+name: System Tests Demo
+
+on:
+  workflow_dispatch:
+
+jobs:
+  run-demos:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        install_gnu_tools: [true, false]
+      exclude:
+        - os: ubuntu-latest
+          install_gnu_tools: true
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+          submodules: recursive
+
+      - name: Install GNU tools on macOS
+        if: matrix.os == 'macos-latest' && matrix.install_gnu_tools == 'true'
+        run: |
+          bin/gnu-install.sh
+
+      - name: Set ASSUME_GNU environment variable
+        run: echo "ASSUME_GNU=${{ matrix.install_gnu_tools }}" >> $GITHUB_ENV
+
+      - name: Run all demos
+        run: demo/all-demos.sh