An unofficial, SET-style matching game you can widen. Give each feature 4, 5 or 6 values instead of 3, and a set grows to match. The table grows too, so there's (almost) always a set on it.
A SET puzzle on a sudoku grid. All 81 cards of the classic deck fit on it once each, laid out so every 3-in-a-row is a set. A few cards are given. Work out the rest.
A set is three cards where color, shape, count and fill are each all the same or all different.
Two cards name the third. Go feature by feature: where the two match, the third matches; where they differ, it takes the value neither has. You never have to guess, because some line always has two cards and one gap.
Keys: arrows move, Q W E color, A S D shape, 1 2 3 count, Z X C fill, Delete clears, Ctrl+Z undoes.