I might be the minority here, but I didn't use any apps for my prereqs (Chemistry, A&P 1&2, Micro, Nutrition, etc). Evernote is touted as a great note taking app, and I do use it for other things, but for school I just take handwritten notes. *shock* I start nursing school in the fall so this might change but I doubt it.
For studying anything, in general, I like www.quizlet.com. That site is free if you stick with text, and only a few dollars if you want to use pictures, too. You log online using a computer to create your virtual flashcards. Various apps are compatible with quizlet so you can view them as flashcards on your phone. On the computer, you can also press a button that will create quizzes for you from the cards Multiple choice, matching, true/false, fill-in-the-blank). I liked using the quiz function the best, but I also used apps to study the flashcards. Quizlet tells you which apps are compatible with it.