Scribblar is a free online collaboration tool that is great for online learning. I really like Scribblar because it is very similar to the basic SMART Notebook software tools (ie pen, shapes, lines etc). It has a simple, user friendly interface. There is also a chat window on the side bar so that users can talk to each other while working. There is even a live chat system if you have a microphone and speakers. Furthermore, once you have created your room (this is what they call a document) you can share it with all of your students without them having to ‘join’ or ‘log in’ with Scribblar. This is a great resource for schools with 1:1 laptop programs.
Beyond the basics:
Scribblar can also support PDF files. Free users can upload PDFs with up to 5 pages. Your uploaded PDF will be turned into an editable image in Scribblar. Source: Educational Technology Guy