1. A distributed group activity network system over a computer network that synchronizes and provides access by system users to shared data files of a group activity, the distributed group activity network system comprising: a server computer that is configured to (a) make basic network services of a standard network protocol available thereat, and (b) store the shared data files and also synchronization files for the group activity; and client computers that are not directly connected to each other or the server computer over the computer network; each specific client computer of the client computers being configured so that, each time a specific user of the system users requests that a selected shared data file of the shared data files be updated at the specific client computer, the specific client computer (a) accesses the synchronization files using the network services available at the server computer so as to determine if the selected shared data file is checked out by another user of the system users and to check out the selected shared data file if the selected shared data file is not checked out, (b) accesses the checked out shared data file using the network services available at the server computer so as to update the shared data file, (c) accesses the synchronization files using the network services available at the server computer so as to check in the updated shared data file, (d) establishes network connections between the specific client and server computers over the computer network in order to perform the accesses, and (e) performs the accesses without using any dedicated processes which may reside on the server computer.