I've just discovered OpenMeetings after some googling.
Features (list taken from its web):
Audio and Video Conferencing
Meeting recording and Screen sharing
File Explorer
With public (conference room) and private (logged user) views
Moderating System
Multi-Whiteboard and Chat
White board with drawing, writing, Drag n' Drop, Resizing, Images
User and room management
Private message center
Plan meetings with integrated calendar
Polls and Votes
Backup
It is a more general piece of software, but it might fulfill your needs.
PS: Or you can just use Skype screen sharing if you don't need to interact remotely with the board. You need to go premium for multiuser video, so probably for screen sharing too.