Put stuff in orbit around Earth and the Moon-Flash game.

[Gemini]

I thought this was fun:
http://www.colorado.edu/physics/2000/applets/satellites.html

[Swift]

I seem to have a very fine ability to get things to escape the Earth-Moon system or to crash on Earth. :shrug:

[ToSeek]

I spent way too much time playing with that one a while back.

[Mellow]

I love this little Java app. What it shows up is how well the Earth-Moon system can sweep up debris.....