1. A programmable workstation for collaborative working in a network in which workstations represent nodes of the network, the network being connected by physical links for supporting communications between nodes, each node including an operating system and application programs, and potentially having at plurality of call manager programs responsible for handling incoming communications which are not specific to a particular application program instance running at the node, wherein only one call manager can be active at a node at any given time; the workstation comprising: a network control program layer, running on the operating system, for controlling physical routing of said communications between nodes; and a collaborative application subsystem for interfacing with the application programs running on the workstation, said collaborative application subsystem being responsive to a predetermined application program call from a call manager program running on the workstation to establish that call manager program as the active call manager program at the node to handle incoming events which are not specific to any application program instance at the node.