Unblock Me is a very famous puzzle game. It's simple and addictive. The goal is to get the red block out of the board by sliding the other blocks out of the way.
Do ruby unblockme.rb. You can play Unblock Me on Colorful Shoes, Red, Green and Purple.
Do ruby make_game.rb. You can make a puzzle by yourself.
A tiny streaming flash video recorded by CamStudio.
Look at Unblock 2.
The sample puzzles, i.e. E050, H050, M050, X050 and X500, are from this site.