regit is a git add-on for managing branch dependencies.
Many github projects are using a pull request based workflow. Developers who believe their feature branch is ready for merging open a pull request, and after some time, someone might or might not press the merged button, and the branch gets merged.
If you now have your branch (let's call it A) PR'ed, and you'd like to do some work based on that branch in another branch (let's call that B), and also PR that, the new PR will contain all the commits from branch A, possibly cluttering the commit list. Now if a reviewer finds a flaw in A that needs fixing, in order to reflect those changes in B, that branch needs to be rebased on A. Not a big deal with just two branches. But if you're trying to keep your PR's small and to the point, you might end up with a lot of interdependend branches, like "driver D needs generic_driver C, which itself depends on core_fix A and B". Now any change to "core_fix A" implies a cascade of manually updating C and D.
regit helps with that.