Today the Apache Foundation released a major update to the open source search engine building tools Lucene and Solr. Version 4.0 adds several new features aimed at making Solr easier to use, more scalable and more customizable.
Although they’re jointly developed, Lucene and Solr are actually two different things. Lucene is just a Java library, not a stand alone search engine. Solr is a search engine server built with Lucene as its core.