BombSquad is a nice minesweeper clone for Mac OS X. The game uses Mac OS X's good looks and its aqua interface and it creates a minesweeper game worthy of a Mac. Other than the slightly different window style, the game looks very similar to its Windows counterpart. The game is free and it works very well.
BombSquad is a game of strategy and logic. You have a grid with a set number of mines in it. When you click on a cell, you turn it and either discover a mine (which finishes the game) or a number. Those numbers represent the quantity of mines that are around that cell. For example, if you uncover a number 1, you know that either above, below, to the sides or diagonally, there is one mine. When there are several numbers next to each other then the game can become easier.
BombSquad has some new features that Minesweeper doesn't have. There is something called a Zap Click, which helps you clear an area after you have successfully determined where the mine is.
In short, BombSquad is a nice strategy game. It is small, light, and lots of fun.
There is a piece called "The truth about Apple and Minesweeper" on the developer's website that is worth reading. I don't think it is true, but it is very funny nonetheless.