Which is the best opensource project which uses lucene extensively?

Either in .net or java.

From stackoverflow

• Does hibernate search count?

  suhair : yes indeed. Thanks

• I believe ScrewTurn Wiki is using it see here for more info.

• Wikipedia uses Lucene, as documented here.

  Karl : Why was this downvoted?

  jamesh : Wikipedia is based upon Mediawiki. Mediwiki is written in PHP; question asks for Java or .NET. There does turn out to be a Lucene extension of Mediawiki, but this answer doesn't give any links to this.

  Avi : Wikipedia is a large open source project, and uses Lucene for search: http://www.mediawiki.org/wiki/Extension:Lucene-search

  Bajji : The information is still relevant to other gawkers in this discussion.

• The Fedora repository software uses Lucene and Solr quite extensively for search implementation, with Fedora's use of extensible content models plugging into Lucene's ability to handle metadata quite gracefully.

• neo4j uses Lucene.

• The products of XWiki too. :)