What are some alternatives?
When comparing Scribblar and Twiddla, you can also consider the following products
Conceptboard - Instant Whiteboards for Teams & Projects
RealtimeBoard - RealtimeBoard is an online collaboration software created as a team collaboration and online brainstorming tool. It's super easy to use & free!
OpenBoard - The OpenBoard software is an interactive white board software.
IDroo - A shared whiteboard for use by multiple Skype-users simultaneously. Features
Groupboard - Free collaborative online whiteboard, web conferencing and online tutoring software that can be embedded in your own website. Used by many online tutors, schools and universities.
Whiteboard Fox - Simple Online Whiteboard