ANts P2P - ANts P2P realizes a third generation P2P net.
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.
Radicale - The Radicale Project is a complete CalDAV (calendar) and CardDAV (contact) server solution.
I2P - The I2P network provides strong privacy protections for communication over the Internet.
DAViCal - DAViCal is a server for calendar sharing.