1. A method for an interactive session between two or more user computers, wherein each of the user computers is operated by a user, the method comprising: storing a data object in a server system; transmitting the data object to at least some of the user computers, wherein at least some of the data object is displayed on the user computers by user client software; and synchronizing the display of at least some of the data object on the user computers, wherein synchronizing comprises: at the server system, receiving one or more Update Messages from one of the user computers, wherein the Update Messages describe a manipulation of the display of at least some of the data object; recording at least some of the Update Messages at the server system; transmitting corresponding Update Messages from the server system to the remaining user computers; and at the remaining user computers, updating the display of at least some of the data object in response to the corresponding Update Messages.