Methods and apparatus for controlling and interacting with devices across a network using a ubiquitous companion. In one implementation, a ubiquitous companion includes: an agent interface for communicating with an agent residing on a host device accessible to the companion, and accessing host device data indicating one or more capabilities of the host device; a command interface for building one or more agent commands according to the host device data and a request selection received from a user through the host device; an output interface for providing feedback to the user through the host device in a format that is adapted according to the host device data; and a controller for controlling interaction among the agent interface, the command interface, and the output interface.