I think the answer, the unmet need Urbit is trying to meet, is "I wish I could install apps on a server as easy as I do on my phone." On your phone, the security comes from a crack team of engineers paid by Google or Apple or MS to make sure no bad apps get in, and on Urbit it would come from Urbit's architecture.

But to be clear, none of those apps exist yet; at this point it's just barely functional enough to start developing real apps.