The problem is, a lot of the platforms that I've liked over the years have been vacuumed up. I still try to use different ones, but it's a lot harder.
I think Digg did it worst.
They all kind of exist, but they were mostly supplanted by bigger, more centralized things. All of them had a part in their own demise, too.
Then in turn those bigger, more centralized things have tended to screw things up.