> The best two examples of this are the Arc browser and Chrome OS. But I think Arc is actually the more interesting of the two experiments. Their first innovation was to break the idea of tabs at the top and instead move it to be a sidebar model.

I will forever hate Arc for popularizing vertical tabs the way they did.

Vertical tabs were a thing since at least the Tree Style Tabs extension (2007), except the Tree Style Tabs were infinitely cooler, because they were a tree, not a list, and right click->open in new tab, would open the new tab as a child of the current tab.

So you could have a hacker news tab during your break, start opening a bunch of articles, read through them, simply un-expand the HN sub-tree, go to work, and then re-expand it during your next break.

Because of Arc, everyone is now implementing vertical tabs, but no one is implementing Tree Style Tabs, and, probably no one ever will again.

Did you know that a custom version of TST is the native tab handling mechanism in Waterfox?

And the latest release also brings back a native RSS reader?

Give it a look. You might like it.

Check out Tabius if you use Chrome. It automatically creates and opens new tabs in a group as you describe in your second to last paragraph.

Fwiw – Orion (webkit) has tree tabs