Sourcegraph: A free code search tool for open source developers (Opensource.com)

Opensource.com introducesSourcegraph. "Sourcegraph is a code search engine and browsing tool that semantically indexes all the open source code available on the web. You can search for code by repository, package, or function and click on fully linked code to read the docs, jump to definitions, and instantly find usage examples. And you can do all of this in your web browser, without having to configure any editor plugin."