Solr, as in ‘Solar’, was originally created by CNET Networks in-house developers, and was released as an open source alternative for on-site search in 2004. Solr indexes your site content, including support for in-document search across PDF and other files, providing your users with results optimised for speed and relevance. With an active development community, there’s plenty of support for using Solr online, as well as continual developments and improvements to the software as it continues to evolve.