Dragon Age Origins - Toolset
Like any editor for a specific game, this will of course be constrained to building more content in the style of the original game. It’s not like you get the graphics engine and can go about creating a FPS from a point-n-click RPG.
Still, for this style of player control, Dragon Age is the best I’ve ever seen and this toolset may divert my attention from Unity3D for a short time. I wonder how much NPC scripting/AI control the toolset gives?
Source: dragonage.bioware.com