Every viewport has a toolbar at the top that is specific to the viewport it's attached to:
Toggle the HuD overlay.
Toggle the turntable on and off.
Display/Hide the hierarchy window.
Display/Hide the properties window.
Toogle the playback_controls.
Set the A/B view control to A only, B only or A/B.
Defines the asset to be used as B for the A/B control. The render settings of the B asset will be used to render it.
Select a predefined camera or a camera embedded in the asset (if possible) for viewing.