I discovered
Blocksum while browsing the Bit Blot (Aquaria) forums. It's a puzzle game similar to Tetris Attack, but with a math twist. You need to put together blocks numbered the same. The twist is that you need to join together as many blocks as the number on each block,
and you can create new blocks by joining adjacent blocks together, which adds the numbers of the joined blocks together. Did that make sense? I had a hard-enough time figuring out the game mechanics, and now I can see why the instructions were unclear. It's hard to describe, although the concept is really not too complicated. When in doubt, use an example. If you join 2 [1] blocks together, you get a double-wide [2] block. If you join that [2] block with a [3] block, you get a [5] block. These can be joined in 4 directions, so you can quickly end up with odd-shaped blocks. In order to make that [5] block disappear, you need to join it to 4 other [5] blocks (for 5 total). That will probably require joining up adjacent blocks to create sums of 5. If you can't find any way to combine digits to make up enough sums of 5, you need to go for higher numbers, and higher numbers of blocks to join. This can quickly get out of hand. There's a saving grace, a "magic" block which will destroy all like-numbered blocks that you join it with. So if you join it to a [5] block], all [5] blocks disappear. It's the only way to keep the game from getting impossible in a big hurry.
I played this for hours yesterday, and only managed a 17000-point max score over about 10 minutes. The last update for the game was in 2006, so I definitely missed out on this one earlier. I do recommend it. The only thing to watch out for is the extremely unintuitive key/button mapping. You can end up with a mess that's hard to work your way out of, because even the directional keys in the menu itself will be screwed up.