Android and iOS
Although not specifically a medical app, Evernote is popular with medical professionals because of its multitude of features allowing you to create thorough notes on patient cases, ideas, events, etc….
Create a note on a patient case, and then snap a photo, annotate the photo with Skitch (by the same developers), record a dictation, attach a file, and share the note with your colleague for a second opinion. You can also download Evernote to your PC or tablet to access all your notes, or do so from Evernote Web online. The search feature allows you to find the note you need, and the app will even search through text within your photos (e.g. a picture of a slide from an in-service you attended). The free version allows you to store 60MB of data per month.