Which corporate messenger to choose?

Question

Messengers

Good afternoon. Which corporate messenger to choose for the enterprise.
The task is this
1) Create accounts and control
2) The server part must support the work of clients via the Internet, that is, branches in other cities must also work with the same
Internet messenger in enterprises without a dedicated channel and ip address, ordinary adsl.
Looking forward to any suggestions or advice

Answer 1

https://slack.com/

Answer 2

openfire + miranda, spar etc

Answer 3

MS Lync Server

Answer 4

hipchat

Answer 5

Openfire server (linux) + Pandion(windows) / Pidgin(Linux) client
everything is controlled, call recordings, plugins, mail checking, transports, file transfer if necessary. if you refine yourself, you can also drive video communication, but you need an intelligent Internet

Answer 6

Look for an example of VIPole - a messenger with AES-256 and RSA-3072 encryption,
there are paid and free versions. And also the possibility of installing a corporate server.
Choose the option you need on the website
https://www.vipole.com/en/features

Answer 7

RetroShare easily breaks through NAT
Tox messenger easily breaks through double NAT
XMPP with OTR
JAMI is still damp but you can use
all of the above is open source I personally tested all these programs