Staircase is a private group messenger built on Cordn: end-to-end encrypted MLS groups
(RFC 9420) whose messages are ordered by a coordinator you choose and carried over Nostr relays. No phone number,
no account on anyone's server, and nobody in the middle can read along.

Group chats with replies, reactions, @mentions, pins and encrypted photos and files
You decide who's in: admins, invite links and QR codes; members join with their own Nostr key
Your keys: a local key or Amber (NIP-55); nothing leaves the device unencrypted
Multi-device: link your phone and desktop to the same groups
Open network: pick your coordinators, relays and Blossom servers
Works with other Cordn clients such as cordn-web; also available for Linux desktop (deb, rpm, Arch)