If I understood it right this is the concept:

Lets say Jerry is an artist (doesn't matter if musician, game developer or what not).
He creates a product (game, painting, music track) but doesn't want to sell it but giving away for free is also a hard time for him because he invested alot of time etc.
So he goes to sellYourRights.com and offers his product.
The concept is:
- If you pay me a total of X dollars I'll release this product for free.
So if he wants, say 100 dollars for the product to be become freeware, and gets 100 customers each paying 1 dollar, or 1 customer paying 100 dollar, the product becomes freeware.

This concept offers a possibilitie for creators to get some money out of their products, for customers to get something for free (if the price is already paid) or spend some money on it and get it when it becomes free.