Stumbled over this on Kickstarter and it looks interesting http://www.kickstarter.com/projects/539087245/spriter i'm not affiliated with thoose guys in any way.. but there is a (windows) beta avaiable to toy around with it.. looks promissing and a native mac version is on shedule.. as an alternative to classic sprite sheets anims surely worth a look, since alot of developers create their own 2d anim system for their games.. plants vs zombies uses such animations.. battleheart from mika too.. hero academy aswell.. well might interest one or the other dev.. cheers