Gamemaker
Gamemaker is a neat program for creating your own games. There is a free version that allows you to create games that you can the pass on to your friends or sell. The full version is only US$19.95 and I think is worth it has it gives you access to more functions. On saying that the free version is still very much worth downlaoded and using. Check out the website for more details.
I have created a couple of games that are free and you can download and play them. Pongball is a 'breakout' type game of hitting the ball into the bricks, destroying them all and then moving on to the next screen. They get harder and intrduce different types of bricks as you progress.
Fix the Holes is a game where you need to solve puzzles by using the fork truck to move pallets of timber over the holes in the floor to repair them. As you complete each screen, the next one will be a little harder.
Click on the image to download each game.