Solr is an open source enterprise search server based on the Lucene Java search library, with XML/HTTP and JSON APIs, hit highlighting, faceted search, caching, replication, a web administration interface and many more features. It runs in a Java servlet container such as Tomcat.
Solr is a standalone enterprise search server with a web-services like API. You put documents in it (called "indexing") via XML over HTTP. You query it via HTTP GET and receive XML results.
* Advanced Full-Text Search Capabilities
* Optimized for High Volume Web Traffic
* Standards Based Open Interfaces - XML and HTTP
* Comprehensive HTML Administration Interfaces
* Server statistics exposed over JMX for monitoring
* Scalability - Efficient Replication to other Solr Search Servers
* Flexible and Adaptable with XML configuration
* Extensible Plugin Architecture
http://lucene.apache.org/solr/
http://lucene.apache.org/solr/features.html