Let me add two other rcs systems to the list. I don't use these, only CVS, and not much of that either. I don't know anything of these rcs systems either, apart from that they exist.

Firstly darcs, which is a simple rcs written in Haskell. I know of it because the Dunkosmiloolump team has won the ICFP 2004 contest and they mention using it at their homepage.

Secondly Corel Versions. It is the versioning system that comes with CorelDraw and Corel WordPerlfect. It is file-based (you save the versions of only one file at once), and you can use it from the shortcut menu in explorer.