Besides being used to build a basic mixer module, you can also use it to add inputs to an existing module, shift levels (say, 1v/oct to Buchla 1.2v/oct), buffer signals... i wind up using 'em all the time for all sorts of things. Gang up a few of them for a Matrix mixer, too?
Also, it has pads for building either with through-hole or (mostly) SMD parts... in case you want to try your hand at SMD before committing to a more complex project.
The circuit itself is based on Ken Stone's Utility mixer (two inverting op-amps in series, so non-inverting overall), shrunk & rearranged to add & extend its features.
Available now (along with my other stuffs) @ http://fluxmonkey.com/pcbDocs/MixChiclet.htm