I've started using Discord[0] with a team, we are pretty happy with it. It's great how you can easily see who's in a call and can join and leave without any cost (you don't have to invite someone to the call, or ask to be invited, etc)
We're testing out Teams at work because of our O365 subscription. About 15 people now. Most seem to like it other than the massive amount of whitespace the chat window takes up. I personally hate the massive animated emojis.
Though a little hokey, it's free for us and people really just want some sort of chat system. I've looked at rocket chat but I'm a jr level sysadmin with CTO/Sr Sysadmin boss in a Windows-only environment.
I'm a little hesitant to let it loose in our 100+ person environment but Skype for Business sucks and Slack would be too expensive.
how about amazon chime
I haven't experienced MS Teams, but Skype 4 Business can go and die in a garbage fire as far as I'm concerned. The mobile client just sucks monumentally, and the desktop client is missing functionality that every other good chat client has had for years.