[ibz]

Nostr is relays + clients.

BlueSky is PDS + relays + clients.

If you look at the history of Nostr and try to really understand the protocol, where it came from and what it was trying to solve, Nostr was also meant to work on a PDS + relay model, except it degenerated to the point where most Nostr app developers are simply writing Javascript browser apps that use relays as a "poor man's cloud", sort of, without any consideration for achieving self-sovereignty of the user.

"I save the data in the 6 most popular Nostr relays and done." is what 99% of the so called "Nostr apps" do. Sounds good in theory, until it is not. Relays were really meant to be treated as ephemeral actors, that come and go, and data was meant to be stored somewhere the user was in control of, but instead, relays are treated as some sort of reincarnation of IPFS, where you save your data and have it safe forever.

Bluesky seems to solve this by introducing the concept of PDS. It's not like PDSes cannot be built for Nostr - there are indeed some Nostr apps that work using the PDS model - save the data in a place the user has complete control of, and then propagate it to relays. The benefit of Bluesky seems to me that it formalizes the concept of PDSes, so that app developers don't have to think about it and cannot mistake the relays for PDSes.