Desktop App
HEY offers desktop apps for Mac, Windows and Linux machines. You can get them here: https://www.hey.com/apps/#mac-windows-and-linux
TIP: If you want to see HEY email and calendar at the same time, just use Cmd/Ctrl+N to create a separate window for the Calendar and Email areas of HEY. You won't have to switch between the two in the same window.