I am self-publishing a free e-book which I make available in several formats: EPUB, online HTML, PDF.
I create (using my own programming scripts) EPUB and online HTML from XHTML sources which I write by hand (in a text editor). Then I also convert EPUB -> PDF using Calibre software.
My question: Except for PDF, which of the other file formats supported by Calibre should I publish too? (For maximum readership of my e-book, provided that some formats may be probably rare and not worth supporting.)