Neverball - an interesting puzzle-arcade game for all ages. You get to balance a ball in hope of picking up the most coins in the shortest time possible. The game is absolutely free and won't cost you a dime, well, except for a large electricity bill as you will be playing this game non-stop!
When you got a couple of minutes free and you want to relax, this game is made especially for those rare occasions. I found this game very relaxing and interesting. There are many levels available to you... some of them are easier than the others, others are extremely hard. You will never run out of levels to play as they are daily developed by active community members of this game, just browse the game's forum to find new levels.
If your computer is somewhat older and can't handle much of 3D graphics, a comprehensive set of settings will allow you to bring the game to bearable conditions and you get to enjoy and relax with this game.
The game is available for all the major operating systems, including Windows, Linux, and Mac OS X starting 10.5. It is important to note that the game's package also installs Neverputt, a game that resembles minigolf.