Citadel
self-hosted, groupware

Citadel is a comprehensive groupware solution that offers a wide range of features including email, calendar, address books, forums, mailing lists, instant messaging, wiki, blog engines, RSS aggregation, and more. It serves as an all-in-one platform for collaboration and communication within organizations, providing users with tools to manage their tasks, appointments, contacts, and discussions efficiently. With Citadel, users can streamline their workflow and enhance productivity by centralizing various communication and organizational functions in a single, integrated environment.