What is the best free alternative to Microsoft Teams ?

Hi guys,

I have a small team working on a idea for startup (ERP system). We are currently looking for a communication application that's free and targeted for developers. So, we checked out Microsoft Teams and that seemed to provide all the functionalities that we needed - Chat rooms, Calling facility , Github support etc. But there seems to be a bug in it. None of the members are able to schedule meetings. That's probably a temporary bug and I have contacted the support already.

Meanwhile, I was wondering what does Dev.to community suggest. Besides Microsoft Teams, Discord and Slack what are the alternatives that would best suit us ?

We are mostly looking for an application that provides - Chat facility , Calls (audio/video) and scheduling meetings. Git support and other developer friendly plugins are a plus but not necessary.

Thanks.