Check out Mondrian: http://mondrian.pentaho.com/ I used it a couple years back at a startup. It's written in Java and IIRC works (only?) with MySQL. Mondrian took a bit of work to get setup, mostly due to my lack of OLAP knowledge at the time, but once setup, it was pretty nice and fast. I think it uses materialized views for the cube data.
I'm actually working on a new project where an OLAP will be nice. Thanks for posting Brewery, I'll definitely give it a spin. OLAP's don't get much love, but are very useful for certain types of problems.