Mando is a human computer interface using a camera and a projector. The camera is calibrated against a projection area to determine the position of physical pointer(pen, LED, laser pointer light...) which is then used to virtually move X11 pointer.
Packages for Ubuntu may be found here: https://launchpad.net/~shoden/+archive/mando
Whyteboard is a painting whiteboard application for Linux and Windows, that allows the annotation of PDF and PostScript documents, and image files with common drawing tools.
Apreta is about sharing information in real-time meetings. It provides desktop sharing, presentation sharing, a shared whiteboard, and audio conferencing.
MeetingPoint is a modular cross-browser realtime collaboration and conferencing environment. It provides Flash web meeting with audio/video conference, shared whiteboard and slideshow presentation, chat, polls, etc. Full Moodle integration.
Java RMI based Collaborative adaptive Whiteboard, Users can be arranged into p2p or superpeer2peer or in fully centralized mode during runtime. Contains everything you expect from a white board like locking, simultaneous access, image sharing etc..