I don't think a stablecoin has been made, or at least if it has it hasn't found wide adoption. That is part of the problem, if people couldn't make profit off of speculating on bitcoin it's quite likely that it wouldn't be as widely accepted/talked about.

It wouldn't be too hard to make a inflationary coin, just mint coins proportional to the estimated GH of the network. That would give the coin a price ceiling.