Here are the top open source and free alternatives to Google search appliance –
- SOLR– Solr is an open source enterprise search platform. It features include full-text search, highlighting, facets, real-time indexing and much more. It would require complete setup from your engineering team for this to be up and running.You can setup your own crawler using nutch.
- Elastic search– They are not really open source (meaning they will make you pay sooner or later). Their paid versions are pretty costly.
- Datapark search engine– DataparkSearch Engine is a full-featured open sources web-based search engine and can be used to search within a website, group of websites, intranet or local system.
- Xapian– Xapian is a free and open-source probabilistic information retrieval library, released under the GNU General Public License. It is a full-text search engine library for programmers.
- Strus-The open source project Strus provides a collection libraries and command line tools written in C++ for building a competitive, scalable full-text search engine.
- Sphinx search–Sphinx is a fulltext F/OSS search engine that provides text search functionality to client applications.
- Manticore Search–Manticore Search is a feature-rich full-text oriented search engine that is fast, reliable and scalable. It is 100% open source project