The apache lucy search engine library delivers high-performance, modular full-text search.

features:
* extremely fast. a single machine can handle millions of documents.
* scalable to multiple machines.
* incremental indexing (addition/deletion of documents to/from an
existing index).
* configurable near-real-time index updates.
* unicode support.
* support for boolean operators and, or, and and not; parenthetical
groupings; prepended +plus and -minus.
* algorithmic selection of relevant excerpts and highlighting of
search terms within excerpts.
* highly customizable query and indexing apis.
* customizable sorting.
* phrase matching.
* stemming.
* stoplists.