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.
I'm a secure-hash-for-content-identification fetishist, so I really like Monotone's approach of naming all versions by their SHA1 hash. Also, despite my experience being almost exclusively with centralized version control like CVS, MS SourceSafe, and SVN, I find systems like Monotone with no inherent central server or canonical version intellectually appealing.
But, since decentralized systems can be harder to explain via a childishly simple model, and can obscure the focal points for casual understanding/contribution, I doubt they will often be the right choice for projects that seek a wide audience. Still, I'd love to see some vociferous advocacy of the Monotone model in the presentation. Also, if any of the tools, especially any visual interfaces, help tame the complexity of a centerless system.
The Monotone docs claim their internal 'netsync' protocol is far more efficient than rsync or Unison, so I'm curious if it is a separable piece applicable elsewhere.