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Skim vs Sioyek: catalog facts
Skim	Sioyek
Free Free and open source under the BSD licence.	Free Free and open source under the GPL. The developer accepts optional donations.
macOS	Windows, macOS, Linux
SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers	Opens a referenced figure, table or citation in an overlay without losing your place Searchable highlights, bookmarks and marks across your whole library
macOS only Notes are stored in Skim's own format unless explicitly embedded	The last tagged release is from December 2022 macOS shows a quarantine warning that needs working around on first launch
Downloadable app	Downloadable app
Open source	Open source
License: BSD-3-Clause	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 22, 2026	Official website Full listing and sources Checked September 21, 2026

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