The once mandatory "visitors chair" in every workspace and most people had two or three.
Folks younger than a certain age miss out knowing the social etiquette relating to visitors chairs, such as stacking "stuff" or coats on your visitor chair is anti-social and very strongly frowned upon. Also it was socially acceptable, standard even, to simply walk into someone's cube and sit down in their (visitor) chair and wait till they could talk, especially if you were (currently) working together on something.
Also "back in the old days" we had intentionally unreservable conference rooms scattered about. So if you needed 6 people on the spur of the moment you simply walked in to the nearest empty room, confident no one reserved it because it was un reservable.
This is pretty much how things were in the early 90s or so. Honestly I don't think I could handle the constant interruption and infinite distraction of an open office, which makes me think about a startup or something; I just can't imagine working in a "modern" office environment. It just sounds horrifying to productivity, like a prison yard or a doctor waiting room or something. Creeeepy.
As a parent when I need to get stuff done at home, like if I'm working at home, I kick everyone out of the room and work in peace and quiet. I never, ever, invite seven neighbor kids over and hand out toy whistles as a gift and nerf toys and then sit in the center of the maelstrom and try to concentrate. Nobody who "works at home" sneaks into a day care center with their laptop to concentrate on their finest work. There's a time and place for that kind of stuff, and its not the workplace.