CommFort, is there an alternative?

Question

linux

Hello.
What can replace this messenger?
- The number of clients is about 20 people.
- Cross-platform (this is the main condition, because the bulk of working PCs on linux)
- The ability to install the server part on your own hardware.
- Free!!!

Answer 1

Jabber\xmpp, implementations of servers darkness, clients darkness in general under any platform. Expands to fit your needs just as easily.
You can also deploy asterisk + sip message. But it is.

Answer 2

Tell us why you didn’t like the options offered by Google on the corresponding request, we’ll discuss.

Answer 3

https://www.mattermost.org/
https://rocket.chat