Inkflow is an iPad app for visual thinkers who like to sketch to process what they're hearing, seeing, and learning. Inkflow can be used to sketch mind maps, draw pictures, write free hand, and just about anything else you might do with a pencil and paper. You can organize your Inkflow pages into books.
There is a free version and a paid version of Inkflow. The free version allows you to use black ink only and your books are limited to twenty pages. But you can have as many books as you want in the free version. The paid version gives you more drawing tools and colors as well as more pages per book. The paid version is now available for volume pricing.
Applications for Education
Two summers ago I read Dan Roam's book The Back of the Napkin. That book turned me on to having students create simple sketches to demonstrate how they understand or interpret a topic. Inkflow could be a great iPad app for students to use to draw sketches and outlines of their understanding of topics that they're studying. Of course, Inkflow could also be used for its intended purpose as a note-taking app.