Hey /selfhosted!

Do you guys know any somewhat reliable and modern messenger for companies that does not require you to purchase license to access full functionality? My company is looking for alternative for Slack as it's becoming very expensive.

I've looked at both Rocketchat and Mattermost and they all have paywalls for advanced functionality, such as SSO or SCIM. At best, it should be something like rocketchat's community edition that they've discontinued not very long ago.

Core functionality I'm looking for is:

1. DM's, private and public channels
   
2. Google SSO or SCIM
   
3. Functionality to import Slack history (not necessarily built-in functionality, might be something from community)
   
4. Mobile apps (well, that may be too much lol)

Thanks!