The environment is based on V8, which provides a lot of tools to sandbox javascript code. There's some other pretty cool technology there - we might write a more detailed blog post about it if folks are interested.
I worked on it for about 6 months and then Apple released Game Center. It was pretty clear that my service would be eclipsed by Game Center so I threw in the towel on it.
At the time, I was targeting Node.js on the server and wrote a fledgling sand-boxing tool called Jefe [1].
I'm using Parse in my current app (Lexatron [2]) and I'm loving it. I'm looking forward to see what I can run on the server side.
Full circle!
p.s. My last name is Lackner. Glad to meet someone else with the unfortunate Lack- prefix.
Another question (just curious): why did you cut node out entirely? libev is awesome and it seems like you would basically have to rewrite if you used straight C++.