We've made substantial progress with STACK over the summer.
In particular, yesterday, I added a "Demonstration" moodle course to our GIT repository.
This contains a number of STACK quizzes in basic mathematics, and once you have STACK 3 working restoring this should be a reasonably straightforward way of seeing the kinds of things STACK is designed to do. It is distributed as part of the STACK GIT repro.
(1) I'm using Moodle 2.4(dev), so the course may not import into a much earlier version. If you have problems please let me know and I'll ponder what to do about it.
(2) If you find some errors with the questions, (I have tried to test them throughly, but they won't be perfect) then please let me know. I'd particularly welcome an exported updated working version if you can manage it, otherwise I'll fix the reference copy myself.
(3) I'd very much welcome any contributions in a similar direction if you have materials you are willing to release.