A collaboration program operates on a computer system for storing, sharing and synchronizing data between different users. Centrally stored content data items are organized by associations into one or more folders, with the folders arranged by associations in a multi-level hierarchical structure. Users have access to all folders and content data items falling within at least one top level folder or “file cabinet” viewable by that user. When a user makes a change/addition to the hierarchical structure, that change/addition is transmitted to a server, which makes the change/addition to the necessary associations and sends messages through a TCP/IP format advising other signed-on users of the change/addition. With each content data item having the capability of being associated into multiple folders and each folder having the capability of being associated into multiple other folders or file cabinets, the computer system operating the collaboration program gives different users simultaneous, synchronized access to the folders and content data items in the hierarchical structure.