Free, open-source alternatives to Vivaldi

Vivaldi is a web browser built on Chromium with a heavily customisable interface: tab stacks and tiling, workspaces, web panels, mouse gestures and command chains, plus a built-in mail client, calendar and feed reader. Vivaldi publishes its changes to Chromium, but the interface layer that makes up the browser's own features is closed source.

The open-source browsers below do the same job of everyday web browsing with extension support. Brave, ungoogled-chromium and Helium are built on Chromium, so most Chrome extensions work in them, while Firefox, Waterfox, Floorp and Zen use Mozilla's Gecko engine and Firefox add-ons. Floorp and Zen come closest to Vivaldi's layout options with workspaces and sidebar features; none of them includes a mail client or calendar.