CrossClj is a tool to explore the interconnected Clojure universe. As an example, you can find all the uses of reduce across all projects, or find all the functions called map. Or you can list all the projects using ring. You can also walk the source code across different projects.
You can also explore Clojurescript (and cljx) projects, such as garden, and browse auto-generated documentation of both standard namespaces or other projects, or do a full-text search on the whole generated documentation archive for all projects.