Urbit is a decentralized personal server platform. The platform seeks to deconstruct the client-server model in favor of a federated network of personal servers in a peer-to-peer network with a consistent digital identity (an ID that remains the same when its underlying public key changes). The design seeks to give users control over their own computing by fixing the underlying issues that cause existing services on the web to centralize, notably: spam, system administration complexity, and development complexity. Overview The Urbit software stack consists of a set of programming languages ("Hoon," a high-level functional programming language, and "Nock," its low-level compiled language); a single-function operating system built on those languages ("Arvo"); a runtime implementation of that operating system ("Vere"), public key infrastructure, built on the Ethereum blockchain ("Azimuth"), for each instance of the operating system to participate in a decentralized network; and the decentralized network itself, an encrypted, peer-to-peer protocol running on top of the User Datagram Protocol. The 128-bit Urbit ID space consists of 256 "galaxies" (2^8), 65,280 "stars" (2^16 - 256 galaxies), 4,294,901,760 "planets" (2^32 - 256 (galaxies) - 65,280 (stars)), and 2^64 - 2^32 "moons" with the rest of the space used for "comets". Each galaxy can spawn 255 stars (2^8 - 1) and each galaxy and star can spawn 65,535 planets (2^16 - 1). Though spawning galaxy planets is currently disabled by Azimuth. In addition, each galaxy, planet, and star can spawn 2^32 - 1 "moons" which are IDs that are subsidiary to the parent's ID. The remaining large amount of address space is for "comets" which exist for use as temporary IDs (keys cannot be rotated) for users to test out the network. Galaxies, Stars, and Planets can all be used on the network as permanent identities, but Galaxies and Stars have additional abilities. Galaxies serve a governance role with each owner getting a vote "on documents and proposals for changes to the Ethereum contracts that govern the Urbit address space." They are also the root nodes of the urbit network hierarchy and today handle all urbit traffic routing. Stars will eventually assist in routing traffic alongside Galaxies, but today they primarily spawn planets and act as the default source of system updates to those planets. Planets are the most common permanent identity - they have keys that can be rotated, but no other special features. Comets can be spawned by anyone via the urbit