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?
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