Bottles and Kegs is a drinking game. The game starts with one player giving a number and a direction in which to count (up or down). The next player then increments by one in that direction, and so on. The caveat is that if the next number has a 7 in it, or it is divisible by 7, you must say 'bottles' instead of the number; if the number has a 5 in it, or it is divisible by 5, you say 'kegs' instead of the number. If both apply (e.g. 35), then you should say 'bottles and kegs'. Any mistake results in a drinking penalty.
Obviously, this is fairly easy if the starting number is small, and dividing by 5 is trivial. But if someone starts at 321, it may not be obvious that the next number (322) is divisible by 7. This is an application that runs on a mobile phone, and solves the problem.
Go to wap.dougalseeley.com on your mobile to download this application directly into your phone. You can download the java files here, but you'll need to transfer them into your phone using the software supplied with your phone.