These days, everybody seems to think that writing Java applets is cool. So, I tried. I couldn't think of anything useful, so I ported one of my early programming deeds, originally created in Pascal on a 512K Mac.
You have to play against the computer. The first player who obtains 5 markers in a row (horizontally, vertically or diagonally) wins. Beware, he's mean!
To start a new game, click Shift-Reload in Netscape.
If you have trouble beating it, have a look at its source code. It is very simple.