You can vote on several game ideas out of a pool of 23, each of them pitched by a Double Fine employee. After 1 week Double Fine will make prototypes out of the top 4 voted ideas.
They will live-stream the creation of the prototypes (about 2-3 weeks) and you will get the 4 prototypes made. (+ steam keys if there will be any)
If you contribute more than $1 you also get Happy Song Prototype and Costume Quest Prototype.
Proceedings go to Child's Play.