monotone is a free distributed version control system.
It provides a simple, single-file transactional version store, with
fully disconnected operation and an efficient peer-to-peer
synchronization protocol. It understands history-sensitive merging,
lightweight branches, integrated code review and 3rd party testing.
It uses cryptographic version naming and client-side RSA certificates.
It has good internationalization support, runs on Linux, Solaris,
Mac OS X, Windows, and other unixes, and is licensed under the GNU GPL.