Unity is the engine used to design, build, and deploy GooBall, one of my favorite time-wasters. What’s interesting about Unity is the development kit runs exclusively on OS X, but you can create games for Windows and Mac. Rarely do we Mac folks get such a deal.
OverTheEdge, or OTEE seems dedicated to making a low-cost yet powerful alternative to game dev tools, which tend to be for the PC only. Oh how I wish Apple would buy 3ds max. Sigh. Some interesting notes in the final release: Unity can create games-in-Widgets. Sweet.
At any rate, I’ve played with it, and I’m impressed. OTEE’s slogan is "Games, Made By You!" and they mean it. Unity is a quick study for anyone familiar with 3ds max or Blender. The documentation is spectacular, and will get you up and running in no time.
Perhaps the most revolutionary thing about Unity is the price: just $250 for the Indie license, and $999 for the Pro. This is introductory (read: early adopter) pricing though, so get it while its hot.