The applet on this page was written in 1997 (and it is amazing that it still works at all!). A newer Pentominos Puzzle Solver, with many more features, can be found at http://math.hws.edu/xJava/PentominosSolver. The new version, however, requires Java 1.4 or higher.
A pentomino consists of five equal-sized squares attached edge-to-edge to form some shape. There are twelve possible pentominos that can be formed in this way (plus their reflections and rotations). In this applet, each piece is represented by a different color.
Consider an 8-by-8 board, consisting of 64 squares. If you select four squares, can the remaining 60 squares be filled in with the twelve pentominos? This Pentominos Puzzle Solver applet will try to solve this puzzle. Note that the applet does not try to be very efficient about finding the solution. It's mainly a demonstration of a simple search technique.
To set up your own board, click on the Clear button. Then select four empty squares by clicking on them. Set the speed of the applet with the pop-up menu in the lower right. After one solution has been found, you can continue the search for another solution by clicking on the Go button.
You can read the source code for this applet. In case you are interested, it illustrates a recursive backtracking algorithm that runs in its own thread.
See my Java page for links to other applets I have written.