IDroo is a free online whiteboard that is
"FREE for non-commercial use
# Collaborative meetings with many participants (10 or even more)
# Insert simple and complex mathematical equations
# Draw and write your ideas
# Express your mind through images
# Take advantage of high quality calls over Skype
# All drawings are easily editable vector graphics
# Works with Wacom Bamboo, Wacom Intuos and other digital tablets"