yours.org actually is the only real competitor for steemit, they will probably arrive on market next year and i suppose they already get prepared to avoid steemit inflation problems and synereo team problems, these two major issues are good examples of what a social platform might avoid.
There is another competitor called seen.life, and they are working with $MEGA, with some support from a youtuber called Lisa Haven, but this initiative is focused on advertisement and tied socially.
Right now, the best initiatives of social blockchain use are: yours.org, belacam and lbry