That concise, plain explanation exists in someone else's words four sentences into the above link:
"Urbit is a new OS and peer-to-peer network that’s simple by design, built to last forever, and 100% owned by its users. Under the hood, Urbit is a clean-slate software stack compact enough that an individual developer can understand and control it completely."
That's what it is. Concise and plain. Why re-explain something that's already well-written by another? Is following links and reading for half a minute too much to ask these days? If so, I'd suggest that the ask isn't very genuine.
