Git is the most widely used version control system, in part because of the popularity of GitHub, a web-based Git repository hosting service, which offers all of the distributed revision control and source code management) functionality of Git as well as adding its own features.
The books featured in this article are all available for free, and many of them are released under an open source license. Some of the text are designed for beginners, others help developers get to grip with the somewhat ugly internals of Git. So get reading, learning and sharing code.