Dialpad (https://www.dialpad.com/ https://www.dialpad.com/) has this feature. Not as a pie chart (last I checked), but at the end of a call, they'll show you a

Dialpad (https://www.dialpad.com/ https://www.dialpad.com/) has this feature. Not as a pie chart (last I checked), but at the end of a call, they'll show you a summary of the call with the speaking time of each participant.