http://github.com/defunkt/resque
http://github.com/mojombo/jekyll
Also: GitHub has released a bunch of open source (as others have added). One of the other things I like is that details of the architecture are discussed openly. When I joined GitHub a few months ago, I was shocked at how much I already knew about how things worked.
Gitorious is 8 million time better than rolling your own git hosting, but GitHub is so much more polished. I think a large part of that is because Gitorious is open source, so there's nobody dedicated to it as a full-time job. Whereas you guys have a handful of developers working night and day on creating pure awesome.
You guys rock.
We do our best to balance features, stability and ubiquity. We consider your data your data, not ours. We've been working on increasing ways to export your data out of GitHub — the new wikis being the latest example — and have a lot of plans on continuing that trend into the future, both through our API and through other efforts.