BitKeeper is a new source management system by Larry McVoy. It handles named branches much in the same way CVS does, but adds extra features (one very important one for major software projects is the ability to have personal repositores as well as authenticated "chains of command"; i.e. Alan Cox could gather a bunch of patches (from other contrubtors) and audit it. What he stumbitted to Linus Torvalds would be seen by Linus sooner (as well as immediately merged into the official sourcetree, if the great LT would allow such a thing).
File names are also handled more gracefully, with version numbers tracking the changes in filenames. It is decentralized and supports working offline.
BitKeeper is published/hosted by Bitmover