iBooks Author - iBooks Author, free from the Mac App store, allows you to create beautiful Multi-Touch textbooks — and just about any other kind of book.
Reedsy - Reedsy is a complete book publishing platform with an elegant, collaborative online editor.
Atavist - Atavist provides a suite of publishing tools to tell stories and build websites.
Book In A Box - Book writing & publishing as a service
Mobipocket eBook Creator - Mobipocket eBook Creator is one of the easiest way to create a professional level of eBooks by simply providing some HTML and image files to your publication.
Tablo - Apple Music for books