Apache Lucene 2.2.0
Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java. It is suitable for nearly any application that requires full-text search, especially cross-platform.
Many new features, optimizations, and bugfixes have been added since 2.1.0, including "point-in-time" searching over NFS, payloads, function queries, and new APIs for pre-analyzed fields. This release includes index format changes that are not readable by older versions. It can both read and update older Lucene indexes. Adding to an index with an older format will cause it to be converted to the newer format.
URL: Apache Lucene - Overview