EDIT: Thank you all for detailing your experience with, and hatred for, this miserable product. Your display of solidarity is inspiring. Now, say it with me:
Same, we had Slack and our company got bought and now we have to use Teams, it's a downgrade in almost every way EXCEPT power automate. I love power automate.
Just about anything. IRC, XMPP, Discord, whatever you call the chat built into Steam. AIM is discontinued now, but it used to be better than Teams is today.