Parallel submodule fetch

git-submodule-fetch

#!/bin/bash

set -e
set -u

if [ $# -eq 0 ]; then
    git submodule -q foreach 'echo $name' | xargs -n 1 -P 10 git-submodule-fetch
else
    while [ $# -gt 0 ]; do
        (cd $1; git fetch -q || echo "Failed to fetch $1">&2)
        /bin/echo -n .
        shift
    done
fi

To complete @ncjones code, and to introduce a tiny bit error management, you could change the cd {}; $* by a cd {} && $* therefore the command $* won't be executed outside of the desired path.