Few months ago, we started a complete rewrite of the new version of Calenda powered by Lodel. The biggest part of the public side of Calenda—programaticaly speaking—is its search engine: this engine is used everywhere, not only on the result pages, but also on the front page and the event page.
Our search engine choice is Lucene/Solr, we already use it to index and provide faceted search on all the contents from Revues.org, Hypotheses.org and the actual Calenda. Solr is fast, powerful, easy to use and to maintain, and supported by a strong community. It also provides a very interesting functionnality: dynamic fields.