What a great game this is. We've had this game sitting on the shelf for a long time now, and broke it out today to play since we all got snowed in.
Blokus is a four player game, but can be played by 2 players. (not quite as fun, though). Each player gets a series of geometric pieces that have strict placement rules: you can't place one of YOUR pieces so that the SIDE of one of you pieces is adjacent to the SIDE of another one of your pieces. The only way you can place a piece is to place it on the CORNER of another one of your pieces. The way to win is to get the most pieces on the board, and you place as many pieces as you possibly can before you run out of combinations.
It's a great game for spatial awareness, puzzle solving, and critical thinking. Fantastic for kids and I would think for teachers as well.
The official
BLOKUS WEBSITE has an applet for playing the game online against AIs or other humans. There's also a
BLOKUS Palm game that is shareware.