OpenDylan (http://opendylan.org) has been using MPS since MPS was first created. (Both were created at the now defunct Harlequin.) We've been working on reviving OpenDylan over the last year as well and this MPS update is a big boon for us.

It's an extremely simple toy intended to help people understand how to integrate the MPS, rather than show it off. But have at it!