Meteor, or MeteorJS, is a 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. It integrates with MongoDB and 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. On the client, Meteor can be used with its own Blaze templating engine, as well as with the Angular or React frameworks.