It was a mac menu bar icon (or systray icon) of a closed eye. You could click on and see a menu of who was "in the room" with you. However, if you hovered or interacted with this menu for a bit, the eye would open on everyone else's screen indicating that someone was "looking around." From this menu you could initiate a chat with whoever was also "in the room"
The whole idea was to try and emulate glancing up from your desk and catching the eye of someone who was also glancing up at the same time, so people wouldn't be interrupting people currently "in the zone" Thus you could create the feeling of working in the same space with people while teleworking, but not have to commit to the definite action of messaging someone in order to feel out whether it was good to talk with a "hey"
I think an always-open connection is good for this too, but I agree that I'd much rather it be audio-only.