I have heard about Lucene a lot, that it\'s one of the best search engine libraries in Java. Is there any similar (as powerful) library for Ruby?
I would try one of them in combination with sphinx.
Thinking Sphinx http://freelancing-god.github.com/ts/en/rails3.html
Riddle http://riddle.freelancing-gods.com/
http://blog.evanweaver.com/files/doc/fauna/ultrasphinx/files/README.html
CLucene is a cross-platform C++ port of Lucene. It can be wrapped and used also from every high-level language (there are also a few legacy Swift projects you could start with). See:
http://sourceforge.net/projects/clucene
http://clucene.git.sourceforge.net/git/gitweb.cgi?p=clucene/clucene;a=summary
Well, there's Ferret, which is a port of Lucene to Ruby. Also, Lucene is very easy to use from JRuby, if that's an option for you.
Depending on your needs, you might also want to take a look at Solr, which is a higher-level front-end built on Lucene. There is a Ruby interface, solr-ruby, that interacts with Solr via HTTP.
Ferret is what you're looking for:
"Ferret is a high-performance, full-featured text search engine library written for Ruby. It is inspired by Apache Lucene Java project."
unfortunately, in most cases, ferret is not what you're looking for, it's got recurring issues with re-indexing speed, index corruption and segfaults on the server. I think most people are going to SOLR, sphinx, and Xapian. I recall seeing some Tsearch / postgres apps mentioned, Tsearch seems to be a industrial-strength solution
Take a look here
Full Text Searching with Rails