I found and played the original creeper world training simulation thingamawhatsit on Kongregate...couple years ago now?
Got addicted enough to it to buy the full version - finding a map editor was a 'bonus'.
When CW2 came out, my husband and I were looking at it and he said something like "Huh, I dunno, its different viewpoint" and I hadn't even looked at the screenshots yet because I was fishing out my credit card....

I found custom maps, code maps, and map editor, all after the fact ;P