(TL;DR: "Urbit also invents a lot of alien technical jargon. We admit that this is annoying. Abstractly, it’s part of the clean-slate program: words smuggle in a lot of assumptions." - to which all I can say myself is: qupnux.)
I guess I'd put it on a poster as: lyrics by blockchain; melody by Xanadu.
Curtis, in his eminent brilliance, was the first of us to realize this, and so became the first of these wise and benevolent engineers, forging a bright path for other open-minded people to follow.
Now come, let's get you changed into this robe and learning these chants. :)
There were no takers.
The question of "but what can you actually do with it?" went unanswered by Urbit's own promoters, even when they were incentivized with real cash money to come up with an answer.
There was also no meaningful documentation at the time, which is why nobody else could complete it.
Also, what does "Urbit's formal semantics makes ships trivial to migrate" mean?
You'd run an Urbit instance (a planet) in the cloud (ideally, on three separate machines where a disk write succeeds if two out of three nodes receive it) and then run sub-instances (moons) on each of your personal computing devices (computers, phone, tablets). You could then interact with your planet and/or moons from your browser.
You'd do this because you want to run cloud-type services like photo sharing and (micro)blogging and such, but you _also_ want to do so through your own UI, not UI controlled by someone else whose interests are disaligned with yours, like Mark Zuckerberg's.
I can't imagine it'd replace standard OSs like Windows, macOS, iOS, and Android.
> Also, what does "Urbit's formal semantics makes ships trivial to migrate" mean?
If you want to move a ship (a directory containing your planet's data) from one (cloud?) computer to another, all you need to do is shut it down, scp it to the new location, and then start it back up again.
The main audience of this post is people who're already into Urbit and understand some of the basic lingo around running a ship. If you don't have that terminology down, and don't know Ethereum either, this probably reads like Jabberwocky[0].