The DMMapp (Digitized Medieval Manuscripts App) links to more than 300 libraries in the world. Each one of these contains medieval manuscripts that can be browsed for free. The DMMapp is developed by the Sexy Codicology Team; it is part of the Digitized Medieval Manuscripts Maps (DMMmaps) project.
For more info, and to use the app. please visit, http://digitizedmedievalmanuscripts.org/app/