People are always saying that you should write down thoughts or sketch ideas as they hit you, because you’re bound to forget them if you wait, even for a little while. There’s just something about seeing those doodles and notes in front of you that makes plans and concepts much more real. A lot of folks I know use a stylus with their tablets or smartphones along with a notepad app to do this. But sometimes, it’s just not the same as using pen on paper or whiteboard pen on whiteboard.
For the latter, there’s Wipebook. It’s essentially a notebook that’s got sheets of whiteboard inside instead of paper. Write, doodle, scribble, take notes, and construct graphs using a dry erase pen, and just wipe the pages clean when you’re done with your notes or change your mind about your ideas.