No one wants to be cramped in a small apartment all day, right? Well, back in the late 19th/early 20th centuries, a lot of people in big cities lived in cramped apartments. Everyone knows that sunlight and fresh air are good for one's health and immune system, including Dr. Luther Emmett, who wrote in his 1884 book The Care and Feeding of Children that it was important to "air" your child to "renew and purify the blood."
So in 1920 we have the Boggins' Window Crib.
And here are a couple actually in use:
Totally safe, right?
I hate that I missed out on this with my first son. However, I have another one due in June, so maybe I can convince the wife to give this a try...