Quick Search Reference Manual for Solr by Mitch Pronschinske.
From the post:
A tweet from Eric Pugh informs us about a recent handy resource he contributed to that you Solr/Lucene users out there should look into.
It’s a Solr reference manual [pdf] based on some distilled references from Apache Solr 3 Enterprise Search Server from Packt Publishing, a book that Eric co-authored with David Smiley. The motivation behind this manual is simply to help with some of the logical inconsistencies in the parameter names (e.g. query type parameter is “qt” but query parser is “deftype”). The reference is meant to help you remember these oddities that are hard to codify in your brain.
Opportunities to improve upon documentation for software are nearly endless. If you like this effort, consider contributing your own.