list-tracked         List all files tracked by vcsh
    list-tracked-by \\
         <repo>          List files tracked by a repository
+   list-untracked \\
+        [<-r>] [<repo>] List all files not tracked by all or one repositories
    pull                 Pull from all vcsh remotes
    push                 Push to vcsh remotes
    rename <repo> \\
        unset VCSH_DIRECTORY
 }
 
+list_untracked() {
+       command -v 'comm' >/dev/null 2>&1 || fatal "Could not find 'comm'"
+
+       temp_file_others=$(mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX") || fatal 'Could not create temp file'
+       temp_file_untracked=$(mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX") || fatal 'Could not create temp file'
+       temp_file_untracked_copy=$(mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX") || fatal 'Could not create temp file'
+
+       # Hack in support for `vcsh list-untracked -r`...
+       directory_opt="--directory"
+       shift 1
+       while getopts "r" flag; do
+               if [ x"$1" = x'-r' ]; then
+                       unset directory_opt
+               fi
+               shift 1
+       done
+       # ...and parse for a potential parameter afterwards. As we shifted things out of $* in during getops, we need to look at $1
+       VCSH_REPO_NAME=$1; export VCSH_REPO_NAME
+
+       if [ -n "$VCSH_REPO_NAME" ]; then
+               list_untracked_helper $VCSH_REPO_NAME
+       else
+               for VCSH_REPO_NAME in $(list); do
+                       list_untracked_helper $VCSH_REPO_NAME
+               done
+       fi
+       cat $temp_file_untracked
+
+       unset directory_opt directory_component
+       rm -f $temp_file_others $temp_file_untracked $temp_file_untracked_copy || fatal 'Could not delete temp files'
+}
+
+list_untracked_helper() {
+       export GIT_DIR="$VCSH_REPO_D/$VCSH_REPO_NAME.git"
+       git ls-files --others "$directory_opt" | (
+               while read line; do
+                       echo "$line"
+                       directory_component=${line%%/*}
+                       [ -d "$directory_component" ] && printf '%s/\n' "$directory_component"
+               done
+               ) | sort -u > $temp_file_others
+       if [ -z "$ran_once" ]; then
+               ran_once=1
+               cp $temp_file_others $temp_file_untracked || fatal 'Could not copy temp file'
+       fi
+       cp $temp_file_untracked $temp_file_untracked_copy || fatal 'Could not copy temp file'
+       comm -12 --nocheck-order $temp_file_others $temp_file_untracked_copy > $temp_file_untracked
+}
+
 rename() {
        git_dir_exists
        [ -d "$GIT_DIR_NEW" ] && fatal "'$GIT_DIR_NEW' exists" 54
 elif [ x"$VCSH_COMMAND" = x'commit' ] ||
      [ x"$VCSH_COMMAND" = x'list'   ] ||
      [ x"$VCSH_COMMAND" = x'list-tracked' ] ||
+     [ x"$VCSH_COMMAND" = x'list-untracked' ] ||
      [ x"$VCSH_COMMAND" = x'pull'   ] ||
      [ x"$VCSH_COMMAND" = x'push'   ]; then
        :