The headline is: Discover some amazing new software. Unleash new potential from your Mac. Support independent Mac developers. And make the world a better place.
For only $39 you up the 13 pieces of software that would normally sell for $626.75 to $975.70 if purchased individually, and 25% of your purchase goes to charity. Currently you get 10 pieces of software. The remaining 3 products are unlocked for others when MacHeist has met their charitable giving goals. For example, all customers will get BoinxTV when MacHeist has raised $400,000 is raised for charity.
I haven't played World of Goo yet, but I've heard enough good things that I'm willing to hand over my money.
The MacHeist webpage explains it all better than I can, so check it out.