UpToDate

UpToDate, Inc.
Android/iOS/Windows
Annual Subscription 

UpToDate is a clinical resource used by many medical professionals which is designed to assist with diagnosis and treatment.

Information is presented in the form of topic reviews, each one addressing a particular clinical issue; those on treatment or management topics include recommendations. Topic reviews contain links to other related topics and are fully illustrated and referenced. You can view related charts, x-rays, photographs, movies and Medline abstracts by clicking on the associated links. There is complete access to an extensive drug database. UpToDate contains the equivalent of 50,000 pages of original, peer-reviewed text. 

This very popular app just released an updated version so some bugs have now been worked out. 

To download, just use the appropriate link:

UpToDate (iOS)

UpToDate (Android) 

UpToDate (Windows)