Do you remember to see a 
smily in OSM in 3D 
Years ago the 3D viewer OSMgo stopped developing. But it is still running as it is. (Wiki)
Soon after the multi-user mode was disabled - mainly because private data concerns. If you use OSMgo as multi-user, all your position and moves are send to the server and to all other multi-users! Of course this is needed to let you see the other users in your 3D view. And on the map too. A green ring will show up on the map at the position of the other “player”. Click on it to join at the same position.
The multi-user mode is enabled again now. But only if you click on the smily in the map popup of the OSMgo map (or if you add &multi=1 to the URL) And you will be asked for a user name; you may use your OSM name. There also is a chat. Press C and write a line to all other multi-users.
Sounds funny Try it with a friend or tell me a time, I may join in. 
The 3D controls of OSMgo are a bit odd. I hate to say it, but a Chromium browser works best. OSMgo was used for many experiments then. And it is far from accurate. I consider to restart 3D rendering, may be in Rust or Zig. Want to help
But before I will study how other (FOSS) 3D renderer are working. May be I will add some documentation to the OSM Wiki pages about building:part etc.
The wiki-page said some roof-shapes are implemented, but i could not find any of them.
