Apache Solr is a high-performance enterprise grade search server with a REST-like API. Documentation is provided to as xml, json or binary. It extends Lucene search library. Ruby/Rails communicates with this awesome search server using the "Sunspot" (sunspot, sunspot_rails gem) library, to do a full-text search. This is a nice tutorial on how to use Solr in your Rails project using Sunspot. Solr:

