Sourcegraph - Sourcegraph is a free, self-hosted code search and intelligence server that helps developers find, review, understand, and debug code. Use it with any Git code host for teams from 1 to 10,000+.
Stack Overflow - Community-based Q&A part of the Stack Exchange platform.
Atlassian Fisheye - With FishEye you can search code, visualize and report on activity and find for commits, files, revisions, or teammates across SVN, Git, Mercurial, CVS and Perforce.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
Krugle - Krugle is the complete enterprise solution for search targeted to the development organization.
Blurtit - Blurtit is a Q&A website. You can ask a question or answer on any question.