In most ways, the now 10-year-old 3DS was an oddity–the next evolution of the equally strange Nintendo DS, and with a trendy 3D hook to boot. While glasses-free 3D was the marquee feature, riding the wave of renewed popularity from 3D films like Avatar, the real killer app was StreetPass. Serving as both enticement to tote your portable system around with you and a bulwark against the encroaching threat of mobile games, StreetPass is a social feature that no other gaming system has ever replicated as successfully, not even Nintendo has done something like it again.
With StreetPass, leaving your 3DS on in sleep mode and taking it with you would ping other 3DS owners doing the same thing, transferring your Mii to their Mii Plaza and vice-versa. This encouraged real-world exploration, especially in more densely-populated urban areas, because you would come home to a Mii Plaza bursting with new friends. It made 3DS owners part of their own little secret club, frequently and anonymously giving each other a handshake.
Sometimes you might recognize someone with wild hair or a very identifiable set of glasses from your bus ride. Checking your Mii Plaza when you got home was a sweet way of realizing that stranger was, in their own way, a kindred spirit. It was an inclusive sense of belonging to the society of “gamers.” The concept was said to have originated from while walking your own canine companion, an activity oriented around getting to know your community.