Seethrough ("Doors", "Open Office") is a logic puzzle, where every cell denotes a "room". The aim is to close some "doors" between rooms. Open doors allow to look into other rooms. The number in the cell indicates the total number of rooms visible in horizontal and vertical direction from that room (the room itself excluded). There can be no isolated rooms; this means that you should be able to reach all rooms by moving horizontally and vertically.
Cross+A can solve puzzles from 4 x 4 to 24 x 24.