faceted tag search

Hello,

Anyone have any good pointers to faceted search examples and plugins.

Flare seems to be defunct. acts_as_solr looks promising but I havent
anything real in terms of features in examples on the web other than
what aaf provides.

I am sure I haven't looked in the right places. I see sites like
http://flippingpad.com/ have implemented a form of faceted search.

Some similar examples and the plugins/techniques used behind these
systems would be very helpful.

*o*
Irfan