Sunspot-client is a project mainly written in Ruby, it's free.
Powerful fulltext search for Ruby objects using Solr - Client Library
Sunspot is a set of libraries that perform powerful abstraction for indexing and search of persistent Ruby objects using Solr. Sunspot integrates with popular Ruby ORMs and exposes powerful fulltext, faceting, geo-search, and other search features, all maintaining a pure-Ruby API. The sunspot-client library exposes Sunspot's runtime search and indexing functionality; it is recommended that this library is used as a dependency directly in production environments, but that the sunspot meta-gem is used in development, as it includes a bundled Solr package that makes bootstrapping local search quick and easy.
Please refer to the Sunspot README for full documentation.