What are the open source code search engines you know about?

Question

I know of google code search http://www.google.com/codesearch and koders http://www.koders.com/ . These two sites help me find usage of some of the libraries, where official documentation of the libraries would go only so far. If you know of some other tools/tips for using these search tools/other tips for finding library usage examples, please share.

Answer 1

http://krugle.com

Answer 2

http://sourceforge.net/

Answer 3

codase

codefetch

Answer 4

Nullege is a search engine for Python source code.