Aha! is a puzzle game in which you get a playing field filled with
different-shaped pieces. If two or more pieces of the same shape are touching,
you can click the mouse on them to make them disappear, which lets other
pieces move into the empty spaces left. The object is to clear the whole
board.

You can adjust the number of different shapes you have to work with (fewer
shapes makes for an easier game) to suit your skill level.