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.
#sourcecontrol
Introduction To Git
A full walk-through introduction to git, from GitHub. Mostly references generic git stuff, rather than focusing on GitHub.
Git
“The entire Pro Git book, written by Scott Chacon and published by Apress”
How to properly use Git with WordPress.org Subversion
How to properly use Git with WordPress.org Subversion
Walks you through setting up a git repo that will interface with a WP.org plugin directory (or any other SVN repo I assume).