_Quatris_ is a puzzle game for one player coded in STOS.
The aim of the game is to stop the quats from filling the play-room. A quat is
a square block and it can be of one of four different types. The quats falls
into the play-room in groups of four (arranged as a square) and they can be
destroyed in two different ways: either by forming a 2×2 box of similar quats
or by forming a line of at least four similar quats (lines may be horizontal,
vertical or diagonal). Forming lines gives more points.
The game ends when the time runs out, or when the play-room gets totally
flooded with quats.