Git is a free & 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.
Anthony Feint has written a great article explaining Why and How Did He Learn Git. And you should also check out Git Immersion, which is a guided tour that walks through the fundamentals of Git, inspired by the premise that to know a thing is to do it.
License: GPL License