Originally Posted by Lisa3
Why won't calibre make it simple - create a calibre viewer app for the iOS and probably for Android, too.......
I once asked Kovid that very question, and his response was that he wishes to make enduring software that will be useful for decades, and he doesn't think a smartphone app is the best use of his time.
Personally, I'm fine with such a succinct answer, because it means he keeps making calibre itself better.
Having said that, you have several options to do what you want. Were you aware that Calibre has a built-in webservice that lets you access your library over the internet from any browser -- including android or iOS ones? On the android side of things (sorry, I don't have an iDevice), there is a calibre app developed by a third party.