You might want to check out braid, formerly known as giston.
I knew about Braid. The way I see it, Braid requires Git. Without it, it is useless. What I want to do with Piston instead is to be completely repository and working copy agnostic. Use the best possible solution given the tools at hand: Subversion properties when appropriate, YAML files if I can’t. Use Git to merge if possible, do it using Subversion if I can’t. And so on.
I even had a request for supporting SVK by Faisal. It will be very important for me to allow any combination of server/working copy. Anyway, more code, less talk. Once I have a workinjg release, you’ll be able to judge the quality of my work.