Freda

Freda is a free program for reading electronic books (ebooks) on Windows. Read over 50,000 public domain classic books, free of charge, from Gutenberg and other on-line catalogs. Or read your own (DRM-free) books in the supported formats: EPUB, MOBI, FB2, HTML and TXT.

The program offers customisable controls, fonts and colours, plus annotations and bookmarks, and the ability to look up dictionary definitions and translations, and (new feature) text-to-speech reading. Freda understands EPUB formatting information (bold/italic text, margins and alignment) and can display images and diagrams in books.
Freda can get books from on-line catalogs like the Gutenberg Project. Or if you have an existing book collection, you can use OneDrive, DropBox or Calibre to share it with your phone. Freda can also download books from any website and from email attachments.
You can download books and keep them on your phone, so you can carry on reading when you don't have network connectivity.

Freda is a free, advertising-supported app, displaying advertising at the bottom of its main page. If you don't want to see advertising, there is an in-app purchase option to remove it.

The manual is at http://www.turnipsoft.co.uk/freda .