Teams are the Best as per Gartner
With so much work being done remotely these days, it's good to see how providers for unified communications systems rank in the Gartner magic quadrant for this field:

The systems cover telephone; meeting; messaging; and mobility systems. Microsoft Teams ranks highest in execution, and is nearly as innovative as RingCentral.
RingCentral's Rainbow system focuses on the use of third party APIs.

8x8 offers messaging systems tailored for specific industries.
