The multipub package, together with external software and some custom scripts, allows you to generate multiple publication formats from a single LaTeX manuscript; currently, the managed formats are a printer-friendly PDF, a PDF version for small-screen eReaders such as the Kindle, an HTML version and an EPUB3 version. With a few tweaks to your original LaTeX document's structure and inclusions, no changes to the source manuscript are required to switch between targets.
Installation of the toolchain requires a Linux machine and is described in detail in the documentation.