OSM Cards is a postcrossing thing for OpenStreetMap members. You get a person's postal address, write them a few encouraging words on a postcard and add a 5-letter code. When received, they type those letters in a form, and the connection is set up.
I announced this website at SotM 2020 and got a few beautiful cards. I lived in Minsk back then and printed like 50 postcards with the city map to send out — and now idk what to do with them :)
Send me one if you like: https://osmcards.org/profile/bqh2on123o
You know OpenWhateverMap.
https://openwhatevermap.xyz/
Grant made the original version, then we lost the domain, and then I updated it with modern tiles and some interactivity: clicking on a tile reveals its name and URL.