Coda:
One way I've seen people describe the blockchain that BitCoin runs on is 'physically distributed, but logically centralised'. Think of the Borg in Star Trek, or the Cylons in Battlestar Galactica; many bodies (apps, wallets, miners, etc), one overmind (the public ledger).
The net, at its deepest level, is the opposite; physically centralised (the fibre "backbone") but logically distributed (many independent servers and clients).
BlueSky is like BitCoin, ActivityPub is like the net.