They succeded in a way, XMPP lost a lot of users back then in the era when communications where migrating from group-focussed IRC to individual-focused Whatsapp (or their respective walled-gardened messengers).
Better than matrix in the ways 2poVoq@slrpnk.net listed above.
It's an open protocol, unlike 99% of chat protocols. It's self-hostable and federated.
It's IRC's successor and been around a long time, first popularized by Jabber. Snikket made it even easier to use.
It was also EEEed by Meta and Google to lure users at a given point, with leads some to say "it's dead" — far from it.
Edit: you may need to ensure OMEO versions are the same across all clients.
The only downside is that Tuta doesn't provide an .onion service as Proton does (although they leak clearnet links left and right)... even though they apparently plan to.
I wonder where are those people archiving data to... i hope it's not US-based servers... just sayin'... hyphanet and IPFS FTW i guess?
The CDC's website meanwhile changed the text to CDC’s website is being modified to comply with President Trump’s Executive Orders., so few that they are...
Joplin synched with syncthing (or Synchthing.fork on android).