Is there something like this for the entire US Code? Laws in the US are often written to say something like "Amend Section X to say Y.", and it's very hard to follow.
I have daydreamed about the same many times and considered trying to start it myself, but it didn't take too long before realizing that the reason I'd want it is the same reason I wouldn't stand a chance at building it. It would certainly be a wonderful resource though. Especially if it could be implemented with a "code review" style interface for showing the votes on each of the bills representing a commit.
I am not sure if there are any for the states.