How does @keychat work? Does it require e-cash for each message sent?
Keychat relay requires ecash sat stamp. Users can also choose free relay. https://image.nostr.build/27854099097f3fbd2f1649f7efe0948993b02a9d34be0cbacd5583d2692cb2fc.jpg
Can non keychat apps pay ecash stamps to write to the keychat relay?
Yes, but the Keychat relay does not accept public notes (kind 1).
Makes sense. Love the stamps model. How do you think about MLS?