Peggle is a very addictive puzzle game by PopCap Games. There are versions of it for Windows, Mac OS X, iOS, and it has been made a Java app and ported to other platforms. The game is very simple, but it can get very challenging after the few first levels. At the beginning of each level, you are given 10 balls. You have to use those to hit "peggles' on the level and clear all the orange ones to complete it. The "peggles" are just little balls that are placed on the background, and their placement change with each level. You move your mouse to aim and shoot one of your balls. When you move it, a trajectory is shown that should help you get a precise shot off. Once the ball is off, it will bounce on all the peggles on the map. So, you have to be careful with your aiming. At the bottom of the screen is a bucket that moves around automatically. If after bouncing around, your ball falls into the bucket, you get it back for another shot.
After the first levels you will start seeing other elements that you have to take out. The second level introduces bricks, which behave differently than peggles, so you have to be adapting all the time.
All in all, this is a great casual game that can be played by anyone. It supports both full-screen and a windowed mode. It has lots of levels and game modes.