BitKeeper!

Mercurial is a free, distributed source control management tool. It efficiently handles projects of any size and offers an easy and intuitive command line interface. Mercurial efficiently handles projects of any size and kind.

Darcs is an advanced revision control system, for source code or other files. It is fully distributed, and supports lazy fetching of the remote repository (fetching only what is needed at the time, rather than all history). It works best with text files, but it can also store binary files.