SeekOut lets you source from several different talent pools.
Public Profile search is an index of over 105 million profiles of professionals across all industries in the US. Each of these professionals has a LinkedIn Profile.
GitHub search lets you find any of the more than 13 million software developers and designers on GitHub.
Social Network search gives you custom search engines for 37 social and professional networks. These sources include more than 400 million profiles and include general purpose social sites like Twitter and Facebook, plus specialized professional sites for healthcare candidates, tech, designers, architects and more.