Downsides of Signal alternatives compared to Signal?

The difficulty of any non-mainstream chat app is getting other people to use it. On that list, Signal is the most probable to be recognized by people who don't have a particular interest in privacy, so it's more likely to get more people to use it.

besides that, and besides the lack of forward secrecy on matrix and session already mentioned by privacy guides, do some of these alternatives have worse security, privacy, or ux than signal in some way?
- both have worse UX than Signal. pretty much all except Signal are lacking on this front. OSS developers are allergic to a smooth UX in general
- Matrix also does have a pretty big problem with meta data. By default it stores a ton of meta data (at least the reference server implementation does) and I am not sure if this is even a solvable problem without redesigning the protocol. When opting for an alternative to Signal, XMPP is probably the better choice.
and how are they ordered in popularity?
- That's a good question. I wonder if there are available user numbers for them.
  I imagine it's regional and depends on what communities you are in. SimpleX chat seems pretty popular these days in privacy circles but I could see something like Briar being useful if traditional networks weren't reliably available for example.

Why is Session always mentioned ? It's an Australian company, in a land with zero constitutional oversight I'd be more inclined to think its a honeypot then a privavy focused chat app. Anom springs to mind as an example.

You should not trust any company or organization. What matters is the security and privacy or the app and service.

What's your use case? Likeminded techie friends? Family members?

Signal works well as an alternative to the likes of Telegram and WhatsApp, even if it still requires a phone number and is centralised. Far easier to explain to the family instead of "oh well you can sign up on this website or this website or that website".

Granted, if you want to host a small Matrix server just for the family, then go for it.

It doesn't require a phone number anymore.
Edit: I was wrong. :p
- As far as I know Signal still requires a phone number to register an account. Since a while you can use usernames to connect with others instead of exchanging phone numbers.

The major one that concerns me is who is behind them. Even if we trust that their encryption is not backdoored, there is a lot of information that can be gathered just from the frequency of messages and who they are between.

If it came out that a three letter agency was running one of these networks, it would not suprise me at all.

https://en.m.wikipedia.org/wiki/Operation_Trojan_Shield

Yeah but you cant really obfuscate your message destination and timing without using onion routing, and really thats just making it more expensive to compromise and run. That said other things here do make it seem like a honeypot...
Its fully open source though, even the server. Might not be that hard to fork it and let people host their own servers.
The only fix for that is for nobody to communicate, ever.
The US military uses Signal for communication

I've had good fortune converting some family and friends to use XMPP.

People always mention fragmentation, and while there is some truth to it, it can be massively minimised by choosing blessed clients and servers for them to use.

In my case, I run my own server, and thoroughly test the clients (especially the onboarding flow) that I expect them to use, so that any question they have, I can help them out with quickly. Since we're all on identically configured servers, it minimises one whole class of incompatibilities.

There is still unfortunately a bit of a usability gap compared to Signal - particularly on the iOS clients. But they have come a long way and are consistently improving.

You can host Simplex server and clients

https://github.com/dessalines/essays/blob/main/why_not_signal.md

I'm using Matrix/element. I rather not give my phone number, you see, which is must-have for Signal. I have installed the app in my family's phones, and they were accepting, so all is well. I don't need to communicate through private messaging with anybody else, so who cares if others don't use matrix?

Yeah, about that. https://www.signal.org/blog/phone-number-privacy-usernames/
- That's my point. The phone number IS STILL required to create an account at Signal!
I think Signal rolled out a username system that should let users communicate without having to share phone numbers
- You still have to register initially with a phone number to be able to setup a username.

Signal isn't federated. Signal has centralized servers. Signal requires phone number identification to use it. Signal stores your encryption key on their servers.... Relying on sgx enclaves to 'protrct' your encryption key.

Signal can go down. Signal knows who you talk to, just by message timing. Signal knows how frequently you talk to someone. Signal can decrypt your traffic by attack their own sgx enclaves and extracting your encryption key.

These are all possible threats and capabilities. You have to decide what tradeoff makes sense to you. Fwiw I still use signal.

Signal stores your encryption key on their servers....
That would surprise me. What's your source for this?
- https://signal.org/blog/secure-value-recovery/
Many assertions without any proof. Could you at least point out the sources for such statements?
- https://github.com/dessalines/essays/blob/main/why_not_signal.md
  Also, most of the points of the message you replied to are abstract and don't need any citation. Like do you want source for signal being centralized or for signal having ability to track you?
- Everything in that post makes perfect sense; the proof is in knowing how these systems work, Signal's source code, and details from Signal themselves. I can go into more detail on each point when I'm at a computer; my phone kills processes in a few seconds when I try to multitask which makes it nearly impossible to write long posts on mobile if I have to go back and forth to copy and paste. Is there any claim in particular you want details on as to why it's reasonable, or shall I just do the lot? Edit: Ah, OP got it, nevermind!
  Also, I should point out that I use Signal pretty much exclusively for messaging. This isn't hate, I'm just aware of its weaknesses.
excuse me what? signal can extract your encryption key how exactly?
- They have your key In a SGX enclave. You only need to look at the rich history of side channel attacks, known SGX critical vulnerabilities, or just the fact that Intel can sign arbitrary code, which can run in the enclave, which means they can be compelled to with the cooperation of the government
  https://dl.acm.org/doi/fullHtml/10.1145/3456631
  https://nvd.nist.gov/vuln/search/results?form_type=Basic&results_type=overview&query=SGX&search_type=all&isCpeNameSearch=false
  I'm not saying they do, but they have the capability, which needs to be accounted for in your threat model.
  At the end of the day, people are entrusting their encryption keys with the signal foundation to be stored in the cloud. That needs to be part of the threat model.
Read the post by signal. Note the use of the word "plaintext".
we don’t have a plaintext record of your contacts, social graph, profile name, location, group memberships, groups titles, group avatars, group attributes, or who is messaging whom.
Whenever someone qualifies a statement like this, without clarifying, it's clear they're trying to obfuscate something.
I don't need to dig into the technical details to know it's not as secure as they like to present themselves.
Thanks. I didn't realize they were so disingenuous. This also explains why they stopped supporting SMS - it didn't transit their servers (they'd have to add code to capture SMS, which people would notice).
They now seem like a honeypot.
- They are very much not. Anyone who tells you this is a state influencer or someone who believed a state influencer.
Signal is still secure. If it wasn't it wouldn't be used in Military applications.
- Secure within the context of a certain threat model.
  The French government does not endorse signal for government communication as an example
  And I would highly suspect the Russian government would not use signal either.
  I cite both of these as examples of threat models that can't ignore some of the potential capability of the signal.

Let's not forget that for those looking for alternatives, a key feature of signal is/was its SMS integration.

I use silence, a fork of signal.

upside: it can still send and receive SMS messages!
downside: nobody else uses it, so it only does SMS as a result.

For those who don't remember, not only could signal be used for SMS, it used to be able to do encrypted sms convos.
Also it sadly hasn't been maintained for years

The need to wait for an SMS to register a new account and the potential for recaptcha loop (which I have experienced) is a serious downside to Signal. Something I never need worry about with xmpp, matrix or threema.

Downsides of Signal alternatives compared to Signal?

I guess that anything out there performs better and faster syncs than Signal... so much for the great Signal.