Arc conceptually merges bookmarks and pinned tabs. Non-pinned tabs are cleared automatically, and you just move a tab above the line to keep it. It's so conducive to the way my brain works, it's not an exaggeration when I say it was a revelation when I first discovered it.

Most browsers try to port the vertical tabs or the split view and proudly say "look, we did it, you can now switch from Arc" but none get this tab concept right, except for Zen which regrettably uses Firefox/Gecko as its base.