Zeitgeist is a service which logs the user's activities and events (files opened, websites visited, conversations held with other people, etc.) and makes relevant information available to other applications. It is able to establish relationships between items based on similarity and usage patterns.

All of the information is stored in one central database for quick access and any application can easily add it's own data to the mix. There are several user interfaces which show the information stored in the database, sorting it by type, date, or relevance to other files. They let users tag documents, bookmark them, and even attach custom notes to each item in the database.