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