A simple-looking block-building game, Blocksum differs in a few regards from other Tetris clones. First, the blocks rise from the bottom, instead of falling from the top. When they fill up the screen to the top, your game is over. Second, instead of matching colors or shapes, you are matching numbers, and a heck of a lot of them. The result is a frenetic and unique puzzle game that will appeal to those with serious Tetris and counting skills.
There aren't any instructions in the game, so you'll have to figure it out for yourself. Here's some help: The default PC keys are Z and X. The arrow keys move your cursor, the Z key lets you join blocks, and the X key speeds up blocks. The object of the game is to match X number of blocks together, where X is the number of the block and how many you need to match. For example to remove a "7" block, you'll need seven "7" blocks touching each other. Any two blocks can be combined, though if it does result in a match, you'll lose those blocks.
The game is much easier to start playing than to explain, and it is awfully addictive. Our only complaints were that there is no difficulty level (once the 9's showed up, we were in trouble), and some confusion about the key controls. The instructions say to use the "A" key instead of "Z," which doesn't work. Aside from some basic presentation issues, Blocksum is a top-class freeware puzzle game.