SBD is designed to be more stable than steem.  The peg to USD isn't strong though, so it has gone much higher and now, lower.  SBD is currently pegged to steem.  Its all quite complicated, but I read about it here https://steemit.com/steem/@buggedout/steem-dollar-peg-to-usd1-usd-is-broken-again-but-not-how-you-might-think