From the web page:
Darcs is a replacement for CVS. Darcs is simple to learn and use, with a powerful new approach to meet the needs of today's distributed software projects. Darcs is decentralized, based on a 'theory of patches' with roots in quantum mechanics.
Written in Haskell, Darcs is used on many operating systems including Linux, Mac OS X, FreeBSD, and Windows.
Darcs is much simpler in use than other systems of similar decentralized designs, such as Tom Lord's arch?. Many of the founders of this wiki use & prefer Darcs; this wiki's software is managed using Darcs.
(Note: As Darcs is written in Haskell, the Glasgow Haskell Compiler is required to compile it. However, there are pre-built binaries available nevertheless; see the web site for details.)