Sigil is a multi-platform WYSIWYG ebook editor. It is designed to edit books in ePub format.
Features
Free and open source software under GPLv3
Multi-platform: runs on Windows, Linux and Mac
Full Unicode support: everything you see in Sigil is in UTF-16
Full EPUB spec support
WYSIWYG editing
Multiple Views: Book View, Code View and Split View
Metadata editor with full support for all possible metadata entries (more than 200) with full descriptions for each
Table Of Contents editor
Multi-level TOC support
Book View fully supports the display of any XHTML document possible under the OPS spec
SVG support
Basic XPGT support
Advanced automatic conversion of all imported documents to Unicode
Currently imports TXT, HTML and EPUB files; more will be added with time
Currently exports EPUB and SGF (Sigil native format); more will be added with time
Embedded HTML Tidy; all imported documents are thoroughly cleaned; changing views cleans the document so no matter how much you screw up your code, it will fix it (usually)
An actually usable user interface
Native C++ application
What’s new in version 2.3.0
New Features
removed support for building Sigil with Qt5 as our code had become a rats nest of qt version ifdefs. See our git branch "qt5final" for the very last buildable version of Sigil under Qt5
our new minium version to build Qt is Qt 6.4.0 or later
removed the need and usage for Qt6Compat5 as its contents were deprecated and will go away eventually
added support for using the ICU library to help replace the range of encodings supported by the old QTextCodec
we are now using NFC unicode normalization form for all content, links, urls, and file paths.
made Sigil's Well-Formed Check (Sanity Check) more robust to whitespace parsing rules and allowed it to detect and report missing XML Headers
we have upgraded to use Qt 6.7.2 and Python 3.11.9 for the base of our Windows and MacOS releases
added a Bookmark Location toolbar icon right beside the Back button for easier use
Opening EditTOC, SpeckcheckEditor or MetaDataEditor will now highlight the first line entry
Add new Tool: Rebase OPF Manifest IDs on Current Filenames
Update to 3rdparty PCRE2 version 10.44 for bug fixes
General code cleanup to remove unneeded hacks and workarounds for old Qt bugs now fixed
Bug Fixes
reverted all Qt Buttons and CheckBoxes to default TabFocus to speed up focus changes and reduce clicks
fixed SelectFiles (AddCover, Insert Image) to again use the arrows keys to walk the list
fixed some lost or stolen focus issues
fix overwriting of existing nav document and cover-image manifest properties
fix for Reports column sorting that use thousands group separators
fix for Reports file size column that did not properly use QLocale for decimal points and separators
fix crashing due to PCRE2 bugs in Qt 6.7.2 with their internal PCRE2
Will sigil ever be compatible with the M1 processor?? I've tried multiple times this year (Nov 12, 2021 today) and it never works. Have a 2020 MacBook Air.
Just a note: This hasn't been a WYSIWYG editor in a while. The dev removed that portion of the app and split it off into a separate app called PageEdit (also open source).
I have used this app only once when Amazon was refusing my book in Calibre's mobi format and it saved my life. :-)
I opened with Sigil the epub generated by Calibre and generated the TOC (Tools/Toc/Generate at that time) then I opened the edited epub in Kindle Previewer or kindlegen and converted to mobi.
So 5 stars for this invaluable tool!