Miro - Scalable, secure, cross-device and enterprise-ready team collaboration tool for distributed teams. Join 2M+ users & 8000+ teams from around the world.
CoSketch - CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images. No registration or plugins required.
OpenBoard - The OpenBoard software is an interactive white board software.
IDroo - A shared whiteboard for use by multiple Skype-users simultaneously. Features
Conceptboard - Instant Whiteboards for Teams & Projects
Scribblar - Scribblar is a free online collaboration tool that is perfect for online tutoring.