Hmm @jb55 said the primal server was proprietary but after looking further I found it here:

GitHub

GitHub - PrimalHQ/primal-server: Primal Server includes membership, discovery and media caching services for Nostr

Primal Server includes membership, discovery and media caching services for Nostr - PrimalHQ/primal-server

I don’t see anyone else running one, but technically relay operators could run this alongside their relay to service Primal users. Although, it feels like a fork of nostr. Users can’t connect to normal nostr relays — therefore it isn’t backwards-compatible. The way we built Nestr was: 1) You can pull notes from normal relays 2) You can only pull the Merkle trees and blossom blobs from blossom servers and HORNET Storage servers We preserved backwards-compatibility. Primal compromised on backwards-compatibility. And there’s literally no documentation on how to change which relays the cache pulls from. 🤦‍♂️ It wasn’t built with other people easily running it in mind.