0x is an open and non-rent seeking protocol that facilitates trustless, low friction exchange of Ethereum-based assets. Developers can use 0x as a platform to build exchange applications on top of (0x.js is a Javascript library for interacting with the 0x protocol). For end users, 0x will be the infrastructure of a wide variety of user-facing applications i.e. 0x Portal, a decentralized application that facilitates trustless trading of Ethereum-based tokens between known counterparties.