Senna is an embeddable fulltext search engine, which you can use in
conjunction with various scripting languages and databases. Senna is
an inverted index based engine, and combines the best of n-gram
indexing and word indexing to achieve fast, precise searches. While
senna codebase is rather compact it is scalable enough to handle large
amounts of data and queries.

WWW: http://qwik.jp/senna/