Can you make the world a better place by playing games? GOSUB 60 thinks so. The company has just released Sudoku Deluxe Green Edition for iPhone (iTunes link) where on-screen actions can turn into real-world benefits.
As you play Sudoku, you can accumulate up to three tree codes. Enter them into the game's Web page, and the game developer will make a donation to Trees for the Future for one tree each. The goal is to plant 100,000 trees. As of this writing, players have entered 63 codes, so get playing.