Keybase already has git integration: https://keybase.io/blog/encrypted-git-for-everyone (now sure why would you want Keybase but okay).

I imagine they meant it's a way to do code review for projects they currently host on Keybase.

Correct, thanks.

Also http://bugseverywhere.org/

And http://mrzv.org/software/artemis (which I use)

BugsEverywhere was broken last time I tried it (one of its git submodules wasn't resolvable IIRC)