Simply pay as little or as much as you fancy on the currently-overloaded 2D Boy site before October 16 to receive a downloadable PC, Mac or Linux version. If you absolutely must try before coughing up even one single cent, nab the demo from FileShack first.
An iPhone version will also join the PC and WiiWare releases. "It's not done and we don't have a release date yet," said the announcement. "We have it running well on the iPhone 3GS, and with a little luck we hope to get it running smoothly on the 3G as well."
"If you played and liked the game but hadn't yet paid for it, this is your chance at redemption!" encourages 2D Boy, referring to the fact 80% of players connecting to the World of Goo leaderboards in the first weeks following release used pirated copies. Co-founder Ron Caramel has called DRM "a waste of time" for preventing piracy.