Methods, systems, and apparatus, including computer programs encoded on computer storage media, for determining other users that will attend an event with a user. One of the methods includes receiving, by a computer-implemented agent for a device, input from a user identifying an event, determining constraints for other users that will be invited to attend the event, determining one or more other users who meet the constraints, identifying, for each of the other users, other computer-implemented agents, each of the other agents for respective other devices, sending, to each of the other agents, a request to determine whether the respective other user of the other agent is interested in attending the event, receiving, from a first subset of the other agents, a response that indicates that the respective other user is interested in attending the event, and facilitating communication between the user and the respective other users.