Excellent online interactive CouchDB view tester

I had seen this before, but it took me a while to track it down again.  This page lets you interactively write map/reduce views against a CouchDB dataset and execute them to see the results.  It's not actually CouchDB, but it mimics it sufficiently to help you get an understanding of views and test various views to help you figure out how to get the results you want.  Very useful!