A comparison between public-domain search engines (PDF, 20 pages) as of March 2006. They compare Nutch, MnoGoSearch, DataparkSearch and ht//Dig.
UPDATE: There is an another comparison of DataparkSearch made in October 2007: Yury Vetrov's blog (in Russian). They compare Sphinx, Tsearch2, DataparkSearch, MnoGoSearch and Yandex.Server (free and commercial versions). Overall weighted rating for these search engines is:
- Sphinx (4,48);
- DataparkSearch (4,33);
- Yandex.Server, free version (4,24);
- Yadex.Server,commercial version (4,09);
- MnoGoSearch (3,82);
- Tsearch2 (3,45).