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Sioyek vs Skim: catalog facts
Sioyek	Skim
Free Free and open source under the GPL. The developer accepts optional donations.	Free Free and open source under the BSD licence.
Windows, macOS, Linux	macOS
Opens a referenced figure, table or citation in an overlay without losing your place Searchable highlights, bookmarks and marks across your whole library	SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers
The last tagged release is from December 2022 macOS shows a quarantine warning that needs working around on first launch	macOS only Notes are stored in Skim's own format unless explicitly embedded
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: BSD-3-Clause
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 22, 2026

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