You can always count on indie game developers to price and distribute their creations inventively. This time, Shacknews writes that 2D Boy is letting folks purchase World of Goo for as much as they want to commemorate the casual puzzle game's first birthday.
The promotion is running until October 16 and applies to the Windows, Mac, and Linux versions. You'd have to cough up $19.99 if you ordered the game from Newegg or Steam, but the promotion lets you get it for next to nothing—or far more, depending how much you like your indie games.
You'll be able to order the game from this page... as soon as the 2D Boy site goes back up. Understandably, word of the deal seems to have taken it off the net for now.
Radiohead tried a similar strategy when it released its album In Rainbows a couple years back. However, subsequent reports revealed that most users (62%, to be precise) chose to pay nothing and get the album for free. The rest paid $6 on average.