bitbucket is a hosting site for the distributed version control systems (DVCS) Git and Mercurial. The service offering includes an issue tracker and wiki, as well as integration with a number of popular services such as Basecamp, Flowdock and Twitter.
Where to begin
If you are entirely new to using bitbucket you should work through the bitbucket 101 tutorial. Wiz kids are welcome to use the search (use the one in the upper left hand corner of the screen), to search. Or use the widget below to browse a list of everything: