[netsharc]

Vivaldi, the Chrome-engined browser made by people who left Opera after it was bought by a dodgy Chinese company, has (like Opera), tabs that are configurable to appear on any side of the window:

https://vivaldi.com/wp-content/themes/vivaldicom-theme/img/f...

from: https://vivaldi.com/features/tab-management/

as well as a open (and closed) tabs manager across all windows: https://help.vivaldi.com/desktop/tabs/window-panel/

I guess I've been using tabs on the side for over 10 years now. IntelliJ also has this feature for open files.