[nickpsecurity]

"4. Has anyone ever built a useful and successful decentralized service. I mean the one that would be popular even if it's centralized, not just like "Facebook but federated". How about starting with this step instead of creating an abstract protocol?"

BitTorrent is the only one that I'm aware of past the core Internet protocols. As I said elsewhere, it spread because of the problems it solved for users in a way they could learn easily. Most probably didn't even know it was decentralized. So, best advice is to solve a problem for users really well with extra benefit of "we also protect your privacy instead of selling you out."

[pherq]

Usenet, back in its heyday, might also qualify

[nickpsecurity]

Oh yeah. It did get a lot of usd at least in the early days.