A Citadel system is made up of containers called “rooms.” A room may be used as an email folder, a discussion forum, a real-time chat, a mailing list, a calendar, an address book, an RSS sink … sometimes a combination of any of the above, and certainly any other uses which could be added in the future. Furthermore, you can replicate rooms between multiple Citadel nodes, allowing you to set up a federated, distributed messaging environment. With that in mind, Citadel excels at applications such as: E-mail and groupware (shared calendaring, etc.) Bulletin Board System (BBS) Online discussion forums / chat rooms The Citadel system is extremely versatile. It provides numerous front ends to present to users, such as a text-based interface, a web-based interface, and many popular PIM clients using SMTP/POP/IMAP. All of these can be used simultaneously.