Crossplatform messengers

So I've been wondering, are there any more secure messengers that work on Linux, Mac, Windows, Android and ios? These are the ones I know:

- Matrix (has clients for every platform)
- XMPP (also has clients for every platform)
- Jami

I don't count services such as Signal, which require a phone to activate the desktop app.

android app clients desktop desktop app don ios linux mac matrix phone platform privacy services signal windows work xmpp