Acidbomb
Acidbomb is a fifty level puzzle game where you must find the pistons used to trigger a bomb and defuse them before time runs out. There are many bombs scattered around the world, from biological bombs that have hair-sensitive triggers to napalm bombs that are exploding at the seams, to nuclear warheads that have challenged even the highest trained bomb defusal agent.

Along with this game you get the Virtual Bomb Simulator which allows you to make your own bombs, and a minigame called Ac!drop that is completely different from the rest of the game...but you'll see that for yourself.

Given that all the bombs in the game have random pistons, you will never EVER solve a bomb the same way twice. Ever. Here's what Gamespy.com had to say about Acidbomb:

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Have you ever wondered what goes through the head of an explosives specialist as he attempts to defuse a bomb before it goes off and kills millions of people? Get ready to find out. This game will have you thinking like the poor dude in all those movies, faced with a nest of wires as a countdown ticks away; he shakes and sweats as he hovers his wire cutters over the red wire ... No, the blue one ... No, the red one!

Acidbomb, or possibly Ac!dbomb, is an intense game reminiscent of Microsoft's Windows staple Minesweeper. Bombs are represented by grids of hexagons. Some of those hexagons are bomb pistons, and some are decoys. Using beams of light that cross the grid, you have to mark which ones are which before the timer counts down to zero.

The game starts with an excellent tutorial that walks you through a few simple practice bombs, and then you're on your own. It's up to you to defuse each bomb before it goes off and spells doom for a building or a few city blocks. As you encounter different types of bombs, you have to visit a training facility to stay mentally prepared for what lies ahead.

This fantastic, free game randomizes the locations of the pistons and the dummies each time you face a bomb, so you'll never defuse the same bomb twice. Strategy and puzzle gamers, and anyone who likes to think while they play, will enjoy every tense second of Acidbomb.