eMule - eMule is a free peer-to-peer file sharing application for Microsoft Windows.
Baïkal - Cal and CardDAV server
Calypso - Calypso is primarily a multi-user, multi-channel reservations system with a wide range of customer and technology driven features and functionalities.
DAViCal - DAViCal is a server for calendar sharing.
Nicotine - SoulSeek client written in Python which uses the PyGTK2 toolkit
SOGo - SOGo is groupware server with a focus on scalability and open standards.