Urbit is a stack that allows for a decentralized filesystem address space created by startup Tlon.
Urbit is a stack consisting of a programming language (Hoon), virtual machine (Nock) and an OS (Arvo) which runs as a Linux app that runs a virtual machine. This virtual machine hosts instances of the operating system called 'identities' or 'ships'. Urbit uses galactic references for components of its system, e.g. a virtual machine, planet (identity on a virtual machine), moon (sub identity space), stars (an address space), planets (64k per star).