A polyomino is a piece made up of squares connected edge-to-edge.
In Game mode, you to put the last piece on the board. The pieces can be flipped or rotated in any manner, and you can use any of the 100 different boards, or create your own.
In Challenge mode, you're provided with a position from the Game mode in which you're challenged to find the winning move. In Jigsaw puzzle mode, you can try to place all the pieces on any of the boards. In Spanning puzzle mode, you try to "span" the board with the fewest number of pieces. The program keeps track of your best efforts.