I originally thought it was only for Cocos. Looks like it has some other major runtimes too. Unity. MonoGame. Even libGDX. :p
Good luck as a mac-only app though.
I think its idea of "Motors" is the most interesting and it seems to be its go-to way of doing stuff.
Looks like "Motors" are actually procedural animation controllers right inside the system that can pull data from its data structures (like curves) and modify its other skeleton parts (like bones and mesh vertices), whereas in Spine, everything's currently just keyed-animated stuff, and you have to do all your procedural stuff yourself in your engine without the help of visual tools. I think the closest thing Spine currently has as a proto-"motor" is IK.
I think going through the different kinds of motors could be very informative.
I think the thing Creature has going for it is that it has a lot of ready-made animation features in it. They're actually quite powerful even if they're potentially inefficient as hell. And with computing power these days, I think it might actually end up a better choice for people who just want to just jump in and make stuff quickly for, say, motion comics or interactive story books or something, where immediately charming animations is important and functional flexibility isn't.
Motion Capture also looks fun.
It's also unfortunate for Creature that it has a number of things not going for it. And for all the cool things it can do and make easy, there doesn't seem to be samples of actual game characters functioning in an actual game environment. That actually makes me wonder how easy it would be to create a functional character skeleton in it and make it actually work in a sidescrolling game, or a top-down game, or an isometric game. It looks like it hasn't gained much of a following enough to have actual game asset animators making demos for it.
Personally, I would love it if Spine had some built-in procedural controllers for stuff like secondary motion that you could adjust and view in the editor. That way, we wouldn't have a million keys and be all silly worrying about key offsets in loops and stuff.
