4digits is a guess-the-number puzzle game. It's also called Bulls and Cows, and in China people simply call it Guess-the-Number. The game's objective is to guess a four-digit number in 8 times.
This little game is very addicting! And you won't need a whole new computer or graphics card to play it. I play it on my Pentium M laptop with Tahrpup. In the view menu there are options to help you figure out the puzzle (without giving away the answers, it's so you won't have to use a pen and paper if you don't have them handy). It's fun, free, and doesn't take too long to play each game. If you like Sudoku or any kind of logic or number problems, you will probably like this.