And would have FOSS implementations of reference server & client + an openly specified protocol.

Like Matrix.

I don't know, the GrapheneOS folks say that F-Droid is a potential security catastrophe.

You can find Molly from Accrescent (and apparently also from F-Droid if you must use that), which is not so much a security catastrophe.

That blog post was my reason to double down on Matrix.

signal requires a phone number and won't even allow you to send sms to those that aren't on signal.

its better, but still not great.

telegram much better

How about Delta Chat? At least as secure as Signal, open source, and decentralized.

Anyone using Session? I finally got most of my friends and family on Signal so I'm not gonna switch but I just heard about it, seems pretty good.

I've been using Signal for years and my database was getting really bloated with media, attachments, etc but I didn't want to delete it all. I used this and it's incredible:

GitHub - bepaald/signalbackup-tools: Tool to work with Signal Backup files.

Tool to work with Signal Backup files. Contribute to bepaald/signalbackup-tools development by creating an account on GitHub.

GitHub (github.com)

Just make a backup from within signal, copy that backup file to your PC, then run this tool. The commands I used make an HTML webpage that looks just like the signal messenger, along with a way of searching your messages. You can choose different commands to export however you like.

I used:

signalbackup-tools [input] [passphrase] --exporthtml [directory] --split --searchpage --originalfilenames

So while this doesn't help you move off your current messenger, you don't have to worry that your data/messages will be lost in Signal.

Basically Signal but without the weakness of a phone number & runs on a Tor-like network. It's still a work-in-progress thing but you CAN use it to send messages

Nah, that would be Matrix, XMPP, DeltaChat or SimpleX

Ya it’d be better if it didn’t require a phone number but it’s a solid start as it’s build up a user base over the past decade. Matrix is good but I know far less people that use it and it’ll be a long time of growing with nerdy/geeky communities before it starts getting more mainstream users

Have a look here: https://www.messenger-matrix.de/messenger-matrix-en.html

I like the comparison and prefer simplex as an replacement to Signal in the Future.
Self hosted Matrix Servers are a good idea aswell if you have the money and knowledge.

Matrix still has it's problems. All the meta data is still saved on every server permanently.

There is still space to improve from there.

By features, yes. By 10 miles.

Privacy? It isn't driving anymore at this point.

any proofs?

Thats a problem with silos (where one owner hosts all the servers) in general. You will have to switch the entire ecosystem once the inevitable enshitification sets in. It's a good idea to switch to something open source and federated (where many different non profit organisations and even self hosting individuals host many different servers).
That way you can migrate your history and contacts to another server of necessary but never have to switch the ecosystem again. Think it how email works, it's the best known federated system. If you don't like you email provider anymore you can just chose another one and still keep your contacts and messages on a client like Thunderbird forever.
Xmpp and matrix are the hottest candidates in my opinion, but you can check the messenger matrix that was linked in a comment above to see what suits you best.

Signal is on F-Droid.

Most of the alternatives mentioned have such low adoption that they aren't truly viable options yet - no matter how much we wish otherwise.

And I say that not as a critic - I actually use Matrix, XMPP, and Jitsi myself. But guess how many of my friends, family, or colleagues are on them?

Exactly.

That’s why I recommend Signal. At least there, people are likely to find folks they already know.

You can save any media you care about. And Signal can backup your chats if that history is important to you.