Finishing (for the moment, at least!) the addition of content for each game I own that hasn't had a BGG review to date.
Four sets of 18 chits (red, yellow, green, purple), comprising one of each digit 0-9, one of each basic operator (+, -, x, /) and four equality (=) symbols. The board is rectangular, 8 x 12.
What Do You Do?
First player lays out a mathematical equality (e.g. "2+3=5", or "5x2-3=7"), running in a straight line in any direction (vertical, horizontal, diagonal). Subsequently, players add their own equality, which MUST include one of the numbers or symbols already on the board. Continue until either one player uses up all their symbols (winner!), or - more likely! - there are no legal moves left, in which case whoever has the least number of chits left is the winner.
There are a few extra rules to make things a fraction more constrained: you can only use "=" once in any equality; you can't play digit-chits next to each other, whether you're using them in an equality or not (operators next to each other is fine, as long as your equality only uses one of them); and you're allowed to skip your turn if you think it advantageous to do so.
This game doesn't tend to last long: the constrained board, plus the lack of repeat chits, doesn't give you much to play with. It's not too bad with kids just starting to get the hang of mathematical expressions, but replayability is low. More chits, and a larger grid, would open things up a lot; from that point of view, something like Tuf has a lot more going for it, but it's aimed at older kids/adults. Certainly for two players, you'd play with two sets of chits each.