Blokus

Blokus is a logic board game featuring a 20 × 20 square board and 4 players with 21 pieces each. The objective of the game is to have the fewest squares left unplaced when none of the players can place any more pieces.

Gameplay
Players take turns placing a single one of their colored pieces, the first one of which must be placed touching one of the corners of the board, and all others must be placed touching corner to corner of another of that player's pieces, but also cannot be touching any sides of that player's pieces.