From a platform perspective, this changes every year, as new technologies emerge, and existing technologies evolve (or don’t).  As of July 2019, Gartner’s global leaders are Microsoft Teams, RingCentral, Cisco, and 8x8.  However, with the speed at which many companies moved to remote work as a result of COVID-19, we expect the top platforms to change when Gartner next does the UC Magic Quadrant.