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

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