Sammy Larbi has done a nice intro to Drools with a simple example Rules-based Programming with JBoss Rules/Drools.
Drools has won an InfoWorld Bossie 🙂 http://www.infoworld.com/slideshow/2007/09/116-best_of_open_so-5.html
Final download stats for Drools in August where:
16293 drools-4.0.0-bin.zip
8364 drools-4.0.0-brms-standalone.zip
7207 drools-4.0.0-src.zip
6978 drools-4.0.0-eclipse.zip
5921 drools-4.0.0-brms.zip
5191 drools-4.0.0-examples.zip