Upspin is an experimental project to build a framework for naming and sharing files and other data securely, uniformly, and globally: a global name system of sorts. It is not a file system, but a set of protocols and reference implementations that can be used to join things like file systems and other storage services to the name space. Performance is not a primary goal. Uniformity and security are.
Documentation
The Upspin Overview document provides a high-level introduction to Upspin.
The Signing up a new user document describes the process for generating keys and registering a user with the Upspin key server.
The Upspin Security document describes Upspin’s security model.