Async Corp. is about as charming as a puzzle game gets. There are a few flaws with it (most notably that the game does a terrible job of actually telling you how to play, but I'll fix that in a second), but it's just so cute and so charmingly devised that it's hard to put down. The idea is that you've got two grids of colored blocks next to each other, and it's your job (in an almost literal sense, as the game's premise casts you as a worker at a fictional corporation) to "pass packets" back and forth by touching one grid and then the other. The trick is that you can only pass packets when they combine up into a rectangular box of four or more, at which point they create cute little boxes with faces on them, which can then be tapped away for points.
There are three different modes to play that challenge you to accomplish things within various limits, but that's basically how the game works. And yes, once you get over that initial learning curve, there's actually a lot of depth to the game: You can trade pieces to create two cute boxes for a "sync" move that earns you extra points, and once you make a box, you can add pieces to it to keep growing it for more points (though every piece you move has to actually finish off the box, so you can only complete them, not build them up).
The game is a lot of fun, and the cute little graphics, excellent chiptune music, and puzzle replayability make it more than worth the 99 cents. Definitely check it out if you're in for some cute puzzle fun.