The NOSTR protocol
This is a convenient compilation of the Nostr protocol specification (https://github.com/nostr-protocol) as a single PDF that is easy to read and print. The protocol comprises a series of nips (Nostr Implementation Possibilities), where NIP-01 is the protocol's base. I set the minimum price for the packaging effort, but you can get it for free.
https://leanpub.com/nostr