Friendica is close, but it’s more federation than social graph. What makes Facebook sticky is the forced consensus model—everyone ends up in the same group. The fediverse avoids that by design. No single instance becomes the center.
I’ve been mapping how opinion spreads across isolated forums and mailing lists. It’s not about engagement, it’s about alignment. If you’re interested: https://thezeitgeistexperiment.com/thread.html?thread=931