Gitslave is a script for coordinated version control of large projects combining code from multiple independent repositories using Git. More flexible than traditional git submodules, gitslave provides a simple wrapper around command-line git that manages a directory tree with multiple subsidiary ("slave") git repositories in sub-directories of a "master" git repository. Any git command run from the "gits" wrapper will be performed in all the git repositories; for example gits checkout -b newbranch will create the new branch in all repositories.
Gitslave has been used for mid-sized product development with many slave repositories (representing different programs and plugins), branches, tags, and developers; and for single-person repositories tracking groups of .emacs and .vim repositories (in the latter case, it is basically used to keep the slave repositories up to date via a single command).
Does exactly what it's supposed to.