When reading a paper, I often find myself furiously flipping back and forth between the text and figures. This is most annoying when reviewing a manuscript, but the typeset pdf often isn't much better. One would think that html versions wouldn't have this problem, but in most cases only a tiny thumbnail is visible, and you have to open a popup or a new browser tab to really take a closer look. This is true even for the well-meaning PubReader format, which successfully replicates the experience of reading a large-print trifold brochure.
But now there's a viewing platform that lets you see figures and articles side by side. Enter Lens. It was originally created for eLife, but is now available for viewing PubMed Central articles with free full texts at Open Access Sandbox. Just search for the article here as you would at PMC.
In Lens, the icons to the right of the text field toggle the right panel between a table of contents, figures, references, and article information. The coolest feature is that everything is hyperlinked. Every reference to figures in the text can be clicked on, which pulls up the relevant image without losing your place in the text. The same is true for references, and it even works in reverse: clicking on the title of a figure or reference highlights all the paragraphs where it appears in the main text on the navigation bar to the left of the screen. You can click on those areas to jump straight to the call out. Article level metrics are said to be on the way, too!