MonoTone is one of the recent crop of OpenSourceDistributedVersionControl systems hoping to replace CVS (see also: SubVersion, GnuArch, DavidsAdvancedRevisionControlSystem, CodeVille, etc.).
Some properties that distinguish it from other systems are extremely distributed operation (designed to easily allow collaboration across trust boundaries, for example, in addition to basics like disconnected commits), cryptographic goodness, simple branching, and powerful merging.