Bounty Market?

I've seen multiple open source bounty markets come and go. Places where I can post a bounty "if someone implemented X using Y, I'll give them $10," and other people could say, "Oh yeah, I'll also add $1 to that bounty!" Or someone could propose, "I'll implement X using Y, if people will give me $11."

Are there any current, lively, active open source bounty markets?