GitHub is a web-based hosting service for projects that use the Git revision control system. It is written in Ruby on Rails by Logical Awesome developers Chris Wanstrath, PJ Hyett, and Tom Preston-Werner. GitHub offers both commercial plans and free accounts for open source projects.
The site provides social networking functionality like feeds, followers and the network graph to display how developers work on their versions of a repository.
GitHub also operates a pastebin-style site at gist.github.com, wikis for the individual repositories and web pages that can be edited through a git repository.
GitHub has a built-in, highly functional Issue Tracker.