Online Challenges

A few months ago I found (I thought through a post here) a site that did buy in challenges and cash prizes for weight loss. I remember looking at it thinking this would be perfect for me but I was in a work crisis so didn't have the time. Now that is over, I am looking for it again and cannot find. Anyone know what I am talking about? It was a site you could buy in whatever you afford, join a group, and everyone who lost over a certain percentage would share the pot.

Thanks for any help!