Algodoo

Here's a couple of planets I made that will explode when they collide with each other.

It uses many small balls attracted to 2 bigger balls(the planet cores) so it uses a lot of computational power, It runs smooth on my E5200 Dual Core 2.5GHZ.

Have fun moving the planets and changing their velocities, you can make some pretty cool effects if you get the planets to orbit each other just right.