BitUSD, the earliest mainstream stablecoin launched in July 2014, lost its peg with the US dollar in November 2018 and hasn't recovered since. BitUSD was designed as the native currency of a platform launched by Daniel Larimer and Charles Hoskinson BitShares. It is collateralized by BitShares tokens.
As BitMEX Research pointed out, BitUSD had a flawed price stability mechanism since it only protects against the scenario where the value of BitShares falls and not when the value of BitUSD falls. The mechanism to hold the $1 peg was psychological.
On Nov. 25 2018, BitUSD triggered an emergency procedure called 'global settlement' because bitUSD was too under-collateralized by BitShares. The event caused a disablement of BitUSD borrowing and the price of BitUSD subsequently collapsed. The circulating supply has also been nearly cut in half in the last four months.