Price: 4.5 BTC, payable to 15pWcAqagHf2EeFjapjWt4EhYWgL5fne7s. Sale ends on Dec. 31.
Anyone seriously interested should contact Curtis Yarvin, the author of Urbit, to broker the sale.
Alternatively: I’ve written a PGP-signed declaration of the sale.  You can simply send the BTC and show it to Mr. Yarvin, who will presumably honor the contract. You might want to ask him first, though.
No refunds or exchanges! Please think carefully before buying.
 Or, to use the author’s new terminology, “aircraft carrier.”