Nostr is great for private groups. 

As in private property   👉   Keys, Community Relays (and media servers, mints, computation...)
Not as in secrecy   👉  nostr:npub1exv22uulqnmlluszc4yk92jhs2e5ajcs6mu3t00a6avzjcalj9csm7d828 
nostr:nevent1qvzqqqqqqypzp22rfmsktmgpk2rtan7zwu00zuzax5maq5dnsu5g3xxvqr2u3pd7qyt8wumn8ghj7mnfv4kzumn0wd68yvfwvdhk6tcpz9mhxue69uhkummnw3ezuamfdejj7qpqnmlgl63nzvdnxtyxxnukwtpdnmd097hgl8dztuzlqk83y5jdq37q3grye2