I've got a soft spot for Live Wallpapers. Some can be functional, others pretty, and some are just fun. The Blocks Live Wallpaper app falls into the "fun" category and according to the author it's "the world's first live wallpaper that turns into a game".
If you're familiar with Tetris you likely pick right up on what this app is all about. When it's your live wallpaper blocks fall and stack, just like the game. Double-tapping on the wallpaper switches you to game mode and let's you participate in the action. When you're done playing just tap the back or home button.
The app comes in two versions, one free and the other paid. The free version gives you most of the same features and game play as the paid version with ads. The paid version adds a few more features and ditches the ads. It's very fun, and very addicting!