I just got VPaint running under Linux and started messing around with it. I made this simple gif of a mass on a spring for starters. I'm no artist, but I think this software has a lot of potential for even someone like me. I look forward to seeing what else I can do with it and what new features will be added.
Thanks, Boris!
Very Simple Gif
Except in the crazzy free Algodoo!while hard(er) in any other software!

A true gem : has some affinities with VPaint!

About the example springs above : http://www.youtube.com/watch?v=-ZelrMxj7X0