Git is a distributed revision control system with an emphasis on speed.
Git is a free and open source, distributed version control system designed to handle everything from small to very large projects with speed and efficiency.
Every Git clone is a full-fledged repository with complete history and full revision tracking capabilities, not dependent on network access or a central server. Branching and merging are fast and easy to do.
More information can be found at http://git-scm.com/