Here's another one of those games that you might remember from your old Atari or Commodore 564 computer.  It's also one of those games that sounds like it should be pretty easy.  And it is - after you put in the time learning the touchy controls.
The goal is simple enough - land your Lunar Module safely on the landing pads.  Of course you have to contend with things like gravity (or the lack thereof) and the fact that your Landing Module just can't seem to keep itself exactly upright...
Use the space bar for the landing thruster and the left/right arrow keys to spin the Lander.  Try to land on the blue landing pads.  Land successfully and you get half your fuel back.
Think you've mastered landing on the moon?  Change the gravity to make it harder.