Have the option to put Tabs on the side of the windows

For windows which only exist in a single tab, like calendar, calculator, Whatsapp, contacts, etc, having tabs at the top works fine. But for a window X, that already has multiple tabs, if you want to group it with windows Y and Z, it gets confusing with all those tabs at the top of the window. 

This becomes a big deal if you want to Groupify a browser with some other windows. A browser can already have 2 rows of tabs, if it uses Tab Stacks. So if you add a Groupy tab on top of that, there will be 3 rows of tabs on top of that window!

Space has a semantics, which we respond to with feelings. So, after a while, those groupy tabs at the top of a window, feel like they are about changing the application, or changing the workspace within an application. 

I would like to be able to put the Groupy tabs at the side. Then I could group together lots of different types of windows, and the spatial semantics would be clear. 

• tabs at the top are for changing the workspace within an application (if it has them)
• tabs at the left side are for changing the application

If you provide this, I will then 'tabify' most of my windows on a laptop screen, so that I can switch around in a more easy way (the taskbar doesn't really do this)