Comes in Pro and Basic versions (Pro supports repository hierarchy, rollback, event triggers). Distributed system, with a repository for each developer. Unix/Linux, MacOSX on PPC and Windows 98 and up. Commercial. http://www.bitkeeper.com/
A client/server configuration management system. The server supports UNIX and Windows NT. The client supports most platforms via command-line, GUI and Web browser-based interfaces. (commercial) (Perforce Software) http://www.perforce.com/
A stream-based software configuration management solution for distributed software development environments includes source code management, change management, software defect and issue tracking. Server runs on Unix/Linux, NT/2000/XP. Client also runs on http://www.accurev.com/
Utility based on the author's "theory of patches" in which they are likened to operators in quantum mechanics. Additionally, every copy of the source is a full repository. Written in Haskell and released under the GNU GPL. http://abridgegame.org/darcs/
Configuration management and version control along with flexible MR tracking to manage changes to software, firmware, hardware, and documentation from origination through maintenance, delivery, and support. (commercial) (Lucent Technologies) http://www.bell-labs.com/project/sablime/
A "next-generation" distributed version control tool. Free, written in Python, and with an interface similar to CVS and Subversion. http://bazaar-ng.org/
Mercurial is a distributed version control system. Mercurial is dedicated to speed and efficiency with a sane user interface. It is written in Python. http://www.selenic.com/mercurial/