Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for using character-driven robots and other agents for volunteer computing and other unengaged time computing tasks. One of the robots is configured to execute instructions that cause the robot to receive one or more sensor inputs from one or more sensor subsystems. From the one or more sensor inputs, a prediction representing a likelihood of one or more users engaging with the robot over a particular subsequent time period is computed. If the computed prediction indicates that the robot is in an unengaged state, the robot selects one or more unengaged time computing tasks and performs the selected one or more unengaged time computing tasks.