MineField - Game that mostly everyone knows. Available on many OS platforms, and now for iPhone as well.
Goal of the game: uncover all squares from 144 that do not contain mines.
The game takes place on the field 16 by 9 squares (144 squares total).
Its up to you to pick the difficulty level, by number of mines - from 5 to 140.
During the game, you can quickly switch either if you want to uncover the square or if you suspect that there is a mine, you can mark it, so you wont accidentally uncover the square and be destroyed.
Rules are simple: touch the square to uncover it. First touch is free - you will never get destroyed at this stage. Whenever you reveal the square that contains the number from 1 to 8 it means that there are 1 - 8 mines underneath the current square. Using this tip try to uncover all the squares.
Its a simple game, fast and without any leaderboard, social, global rankings. Play it when you have plenty of free time, or if you are only waiting for the bus.