Git submodule init async

Linux:

cat .gitmodules | grep -Po '".*"' | sed 's/.\(.\+\).$/\1/' | while sleep 0.1 && read line; do git submodule update --init $line & done

Mac:

cat .gitmodules | grep -o '".*"' | cut -d '"' -f 2 | while sleep 0.1 && read line; do git submodule update --init $line & done

As of Git 2.8 you can do this:

git submodule update --init --jobs 4

where 4 is the number of submodules to download in parallel.