it looks like there's a bunch of stuff out there that this doesn't find. it seems limited to specific silos like github and so on. the debian code search, on the other hand, has access to all software shipped with debian: https://codesearch.debian.net/ this is arguably another silo, but the diversity of software in there is also interesting.
It does however index the following (and more) repository locations, Github, Bitbucket, Fedora Project, Google Code, CodePlex, Sourceforge, Tizen Project, Google Android, Minix3, Seek Quarry, Gitorious and a collection of sources from GNU Savannah.
Im always looking to add more, so if you know of say a github for fossil projects (tarpit would be an excellent name for this BTW) let me know so I can add and index them.