Free Scriptures: Convert OSIS files to EPUB

EPUB is an openly specified standard with a long history, but mostly specified by the IDPF and now W3C. It's for "e-publications", especially for reading, transfer, archiving and offline use of electronic text. The beauty of it is that the format is heavily based on web technology, so EPUB files are little more than .zip files with XHTML in them (zipped websites that contain all elements/resources of the site). The most prominent use of the format is for what people call "e-books", be it on the phone, tablet or dedicated e-ink device (the latter are the ones with extremely long battery span, because the e-ink display only needs very little power to change a page and then it stays as it is without active power consumption), but in context of the web it must not be the only one.

PDF, on the other hand, is designed for printing, not for reading on a screen, writing, annotating or whatever else (sure, Adobe wants to tell you otherwise).