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, has no external 
dependencies, runs on linux, solaris, OSX, windows, and other unixes, 
and is licensed under the GNU GPL. 

Monotone requires Botan and Lua for building.