The main difference between #Cordn and #Concord is that Cordn is based upon MLS and therefore has a coordinator server and forward secrecy, while Concord is client-relay-client. Concord is not as secret (if the key leaks, everyone can read everything from that epoch, and keys aren't associated with devices, so they're easy to share with people outside the group), but it's able to handle larger groups with less overhead, and you don't need to run a server. (You don't need to run one with Cordn, either, as you can use existing coordinators, but there are more relays than coordinators.) Concord seems to be aiming more at the Discord market, and Cordn is aiming more at Signal. I am going to implement Cordn in my Imwald Android app once it's a bit more mature and just not bother ever implementing DMs (since 2 people in a Cordn room is effectively the same as a DM). HTH