I've used Calibre for years and I like it a lot. It quite good for creating or editing e-books (oh the ghastly things you see if you look inside an e-book...)

I've used Calibre for years and I like it a lot. It quite good for creating or editing e-books (oh the ghastly things you see if you look inside an e-book...) The Calibre UX is fine. The real UX divide isn't desktops / laptops vs. smartphones / tablets, but rather content creators vs. content consumers. Modern UX is oriented to content consumers but even there manages to waste too much space and has become too flat and minimal. But once your application is at least partly for content creators, a dense interface is ideal and comforting. I've haven't experienced any data loss with Calibre except when the e-book editor crashes while checking a book for errors. This has always been due to memory exhaustion (2 GB limit) when checking books that were unnecessarily complex (see “ghastly things” above). SumatraPDF opens EPUBs almost instantaneously, but at the cost of not rendering every aspect correctly. As I recall the documentation is clear about this limitation. I like the PocketBook app a lot and use it to read books on smartphones. But it has some basic rendering quirks; for example it can ignore margin-top and margin-bottom on paragraphs, seemingly because it does not apply CSS precedence rules correctly. It took me five e-mail exchanges, including sending a very simple hand-rolled EPUB illustrating the problem, to convince the developers that there is a problem.