This package is the heart of Meteor's Hot Code Push functionality. It has a client component and a server component component. The client component uses a DDP API provided by the server to subscribe to the version ID of the most recent build of the app's client. When it sees that a new version is available, it uses the reload package (if included in the app) to gracefully save the app's state and reload it in place.
autoupdate is part of the Webapp
project.