Interactive Illimitably is a free collaborative drawing tool that I learned about through a comment on my post of 11 collaborative drawing tools. Interactive Illimitably provides a place for you to create a room with a custom name in which you can draw and chat with others. To get started just select a chat font style, name your room, and specify if you want your room to allow drawing, chatting or both. To have people join your drawing and chatting room, just give them the link assigned to your room. While there is a registration option, you don't need to register to use the site.
Applications for Education
Interactive Illimitably could be used by students to collaborate on the creation of story webs. Students could also use the service to collaborate on the creation of diagrams to use in presentations that they give to their classmates.