I, personally, would consider only Jami, qTox (tox), Signal or Riot (matrix), if you're seeking privacy.
however all have their problems.
Signal - (uses signal proctocol - opensource)is great on mobile, and it's growing in users very fast. However the desktop client is a bit awkward (IMHO) as it's not a native software (i think it used to use electron...). It's regarded (and awarded) as the best alternative for privacy to whatsup-like apps. It's centralized, but very few metadata is recorded (i think only the day of the first connection is recorded...)
qTox - (uses tox proctocol - opensource)is very nice as well, but not much used and the development seems stagnated and not much is heard about it either. Mobile version is also not very active. The tech behind it is great, however. It's a Distribuited System - so it does not need servers to work
Jami - (unsure what its protocol is called - opensource)is a great software no one knows about and few use it (yes, the good old chicken and egg problem). That apart, it is a distributed system (like tox, but i have the feeling jami is superior in it's implementation - but i could be very wrong about this feeling!!!!) so it also does not need servers.
Riot - (uses Matrix proctocol - opensource) very promissing as they are running toward making it use P2P communications - and so, making matrix a distributed service (no need for servers) like jami and qtox - but... it's only on beta stage and... well it may take a while... ( https://matrix.org/blog/2020/06/02/introducing-p-2-p-matrix ) but, on the bright side, unlike jami and qtox, matrix is much used by many projects (KDE guys, for example, decided to adopt it across their entire project).
So, for something that works cross-platform, i would bet on matrix on the long term, if you need a service that many people use, or Jami, if you don't need it to be used by outsiders.
qTox seems too much stagnated for me. Signal - while it's a great service it's centralized AND i - PERSONALLY - don't like their desktop approach (i maybe outdated and not knowing if they already have a decent, native, software for Linux/windows/macos desktops)....... IT'S THE BEST ON MOBILE, HOWEVER - VERY VERY GOOD!!!