2D boy seems to have lost its mind a bit in celebrating the first year anniversary for the much-praised puzzler World of Goo. At present the company's website is selling the PC, Mac and Linux versions of the game for whatever the heck you feel like paying until Monday, October 19.
The site has been on an offline and varying in its speed all day, presumably due to awesomeness -- indeed, they do love you, 2D Boy. However, the main game page should be good to go.
It should be noted the company is rather progressive in its views on DRM (World of Goo has none), so not only for that we recommend a sizeable amount for this underloved but lovely game.
Also: an iPhone version is in the works and should be ready relatively soon.