Hi, Sigil is a free, open source, multi-platform ebook editor. It is designed to edit books in ePub format (both ePub 2 and ePub 3).
If you don't have any ebooks to test with, https://standardebooks.org/ has a number of public domain works in both ePub 2 and ePub 3 formats. ok? -- Anthony J. Bentley
sigil.tar.gz
Description: sigil.tar.gz
