I wrote about SVK in Mirror, mirror on the wall and Going local with SVK. Now the release of version 2 has been announced. Note: WIN32 binaries are not yet available.
What is SVK? A quote from the homepage: svk is a decentralized version control system built with the robust Subversion filesystem. It supports repository mirroring, disconnected operation, history-sensitive merging, and integrates with other version control systems, as well as popular visual merge tools.