Undermined is an open source Minesweeper game available for Mac OS X Dashboard, offering an appealing interface. This software is licensed under BSD License terms for distribution and use.
The best part is that it works within the Mac OS X Dashboard, so you can easily access and play it whenever you want. To top it off, Undermined is free to use and distribute under the BSD License, so you can even share it with all of your Minesweeper-loving friends.
Overall, I highly recommend giving Undermined a try - it's a great Minesweeper experience that you won't want to miss out on.