Meteor, or MeteorJS, (formerly known as Skybreak) is a partly proprietary, mostly free and open source isomorphic JavaScript web framework written using Node.js. Meteor allows for rapid prototyping and produces cross-platform (Android, iOS, Web) code. The server-side MongoDB program is the only proprietary component of Meteor and is part of the Meteor download bundle. It is possible to use Meteor without using the server-side MongoDB. It uses the Distributed Data Protocol and a publish–subscribe pattern to automatically propagate data changes to clients without requiring the developer to write any synchronization code.