This page documents plugins, libraries, bindings, and modules that exist for the explicit purpose of integrating Solr with other applications (third party, or user created). You may also be interested in the SolrEcosystem which documents other Information Retrieval projects that relate to, or may be used with, Solr.
Solr Client Libraries / Language Bindings
Java - SolrJ
Scala - scalikesolr
JSON - SolJSON
Integrating Solr With Other (Non Search) Applications
ColdFusion - ColdFusion 9 now includes Apache Solr
Drupal - A Drupal module that integrates Apache Solr in Drupal.
eZ Find - eZ Find, a solid solr integration to the open source CMS eZ Publish
Foswiki - A Foswiki plugin that integrates Apache Solr in Foswiki.
Various Library Catalog Applications - Solr4Lib
Woltlab Community Framework - A WCF package working with the burning board, the blog and all other WCF components.