The Amazon Appstore is running "$100 in free apps" special yesterday and today. While most offerings are mediocre, Essential Anatomy 3 is fantastic. It's huge but can be moved to sdcard. It allows you to view in 3D a human, adding and removing all systems (lymphatic, nervous, digestive, muscular-multiple levels, connective, etc.), rotate and zoom, make specific parts stand out by making its neighbors vanish, select and mark for sharing an image, and more. It's one of the best apps I've gotten bar none.