^After days of downloading free CAD software after another...
   looking at complicated animation, trying to decipher physics
   code I'm unfamiliar with, I came across this. It's the simple
   but accurate enough tool I was looking for to draw and animate
   ideas. If you like happywheels - or even if you don't... this is
   the same kind of thing. And it's fun because, well, it does what
   you tell it to do.^