An activity-based collaboration system provides communication and other shared and mutual activities between individuals and small groups in shared private spaces, called “telespaces”. In the system, participants or members of a telespace interact through personal computers, Internet appliances or other network-capable devices, which can communicate with one-another over a network, e.g., the Internet. Each telespace is an instantiation of an activity operable on each of the network-capable devices of members of the telespace. Each activity includes a tool for initiating data change requests (called “deltas”) responsive to telespace member interactions, and a data-change engine, separate from the tool, for maintaining telespace data pursuant to a common data model, usually activity-specific, in memory. Each network-capable device also includes a dynamics manager, responsive to the deltas, for directing the data-change engine to make changes to the local copy of data.