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.
Perl/Gtk+-based browser application for monotone databases
A Qt-based cross-platform GUI for monotone
A Gtk+-based application to visualize monotone ancestry graphs