Babbler now uses Git instead of Mercurial. Admittedly I have no extensive experience with either source control system, but judging from my limited experience with both systems, I feel Git is more suited.
In my opinion working with Git's branching model feels more natural, the tools for modifying history are better integrated (no need to install extensions) and the documentation is written more comprehensively.
So, let's give it a try!
The old Mercurial repository is still available here, but will probably be removed in the future.