I must admit I was quite impressed by this project: http://www.cgsource.net/jetcraft.html#/general/

In-game map editor, you can test/play your designed levels, save/load them, etc.
It's superbly rendered with custom models and quite a lot of different items (coins, traps, switches, terrain, you name it!).

Anyways, just felt like throwing this out here.

Yeah I saw this, I think he is letting you download it to look at in the weekly triggering excersice on sc2mapster, not sure if that is where you saw it xD But yeah, its freakin amazing =O