Abstract: Actions from multiple devices are synchronized to generate a representation that may be used for collaboration. Synchronization may include a roll-back procedure that allows an action on the representation, which may have been performed by another device at an earlier time, to be included in the representation. Also, a non-user of an application may be invited to use the application through an automated procedure that downloads and installs the application and establishes communication with the sender of the invitation, causing the new user to have an up-to-date representation. The automated procedure may be invoked by a single click on the invitation.