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Kotobee Author vs Sigil: catalog facts
Kotobee Author	Sigil
Freemium Free license and a 30-day trial are available, with paid plans for more features.	Free Free and open source under the GPL.
Windows, macOS, Linux	Windows, macOS, Linux
Exports to EPUB, HTML5, desktop and mobile apps SCORM and LTI export for learning management systems	Edits EPUB 2 and EPUB 3 in a visual view or directly in the XHTML Built-in validation catches the errors that make readers reject a book
Advanced publishing and distribution features sit in paid plans Aimed at publishers and educators, more than a simple ebook converter needs	EPUB only; it does not handle MOBI, AZW3 or PDF Some XHTML and CSS knowledge is needed to fix anything non-trivial
Downloadable app	Downloadable app
Closed source	Open source
License not stated	License: GPL-3.0
Not stated if an account is needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 24, 2026	Official website Full listing and sources Checked September 21, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.