Simple game development engines

I haven't looked at the API yet, so I couldn't say.

Something else:
http://www.stencyl.com/ isn't out yet but it's something to watch.

http://www.simscarnival.com/ is.. something? Supposedly a web-based game creation system with a sims coat. I signed up but I haven't been let into the beta yet.

http://www.rtsoft.com/novashell/ is available but lacks some features as of yet. It's really easy to build something though.