If the e-book app on your phone or tablet is overflowing and full of outdated files, use these tools to tidy it up.

The book is peppered with illustrations, flowcharts, lists, labelled diagrams, infographics and colour-coded code. Some images repeat over several pages, adding extra information every time.

Forget flash – the computers of the future might store data in DNA. George Church of the Wyss Institute at Harvard University and colleagues have encoded a 53,400-word book, 11 JPG images and a ...