This is a branched version of Sigil that based on version 0.3.4 and developed by Si-Wei Wang.
The difference between this version and original one is only on EPUB 3.0 feature supporting.
This version is located here: https://sourceforge.net/p/sigil4epub3
All the constrains are the same as its original version described as follow:
===============================================================================
Sigil is a free, open source, multi-platform WYSIWYG ebook editor.
It is designed to edit books in ePub format. The version of the package
can be found in the ChangeLog.txt file.
It's website is located here: http://code.google.com/p/sigil/
The src directory contains all of the source code. It has
a few subdirectories:
src/BoostParts - source code of various parts of the Boost C++
Libraries that Sigil uses
src/Sigil - source code for the Sigil application
src/libTidy - source code for HTML Tidy, an HTML cleaner
src/ZipArchive - source code for ZipArchive, a zipping library
The installer directory contains the files needed to produce
a binary installer for Windows and Linux.
The manual directory contains the manual in reStructuredText format,
designed to be preprocessed with Sphinx.
The INSTALL.txt file contains information on building Sigil from
source code (and installing it on Linux machines).
The GPLv3 license under which Sigil is released is located in
the file called COPYING.txt.