A facility for managing information about document-related activities is described. In some cases, the facility uses particular kinds of structures to represent, in a document graph, document-related activities performed by particular users. In some cases, the facility uses these structures to enable one user to subscribe to the document-related activities performed by another user. In some cases, the facility uses these structures to aggregate document-related activities performed by users in a group of users, such as by aggregating topics that are addressed by documents that are the subject of these document-related activities. In some cases, the facility uses particular kinds of structures to represent, in a document graph, tasks that certain users either can help with or need help with. In some cases, the facility uses these structures to match users that can help with a task with users that need help with a task.