GIT would come closest. Note that while it's not common now (aside from some first canaries, like scuttlebutt), GIT works perfectly fine as a P2P opennet. You are much less trapped on github, because you can just take your repo and the complete history in it anywhere you want - be it central server, or some sort of P2P overlay.
Isn't Darcs based on some kind of "theory of patches" too? That was the whole selling point versus Git, that Git takes snapshots and calculates diffs, while Darcs takes diffs and calculates snapshots.
