The Tlon app is literally just a messaging app. But behind the scenes, everything is running on your own urbit that you can self host if you wish.
Urbit is a new operating system built from the ground up. The basic gist is a solution to the problem of collapse and tech debt as seen here https://youtu.be/ZSRHeXYDLko?si=Xh2uOLLR9it2CWms
An operating system that you own needs to be an operating system that is potentially understood by just one person. I like to think of Urbit as the Volvo of computers. Take it apart with just one set of wrenches.
Everything is “kelvin versioned” meaning it will eventually reach version zero where it never changes ever again. This is just fundamentally different from every other project in existence