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Sleipnir vs Vivaldi: catalog facts
Sleipnir	Vivaldi
Free Free to download and use. The software is closed source.	Free Free, funded by default search engine and bookmark placement deals.
Windows, macOS	Windows, macOS, Linux, Android, iOS
Right-button mouse gestures cover most navigation, and the tab thumbnails stay usable even with a hundred tabs open.	Tab stacking, tiling and vertical tabs without a single extension Built-in mail, calendar and feed reader in a side panel
It is closed source, the documentation is largely Japanese, and the macOS build was paused over a Tahoe…	Not open source; only the modified Chromium parts are published The sheer number of settings takes real time to work through
Downloadable app	Downloadable app
Closed source	Closed source
License not stated	License not stated
Not stated if an account is needed	No account needed
Not stated if it works offline	Needs internet
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.