From the National Library of Medicine:
The National Library of Medicine (NLM) is pleased to announce the implementation of the Universal Viewer for examining the thousands of digitized texts on the Digital Collections web site. Universal Viewer is an open-source community-supported software developed by Digirati for the Wellcome Library and the British Library.
The NLM Digital Repository Working Group selected Universal Viewer after an in-depth software evaluation. Universal Viewer fits easily with the existing applications Digital Collections uses to present high-quality page images through the International Image Interoperability Framework (IIIF), Loris image server and Blacklight discovery layer.