Early versions of Opera (maybe 20 years ago or so, I don't remember when exactly) had real MDI, where the tabs were subwindows rather than actual tabs. You could arrange them however you wanted, tile, cascade, etc.
For me, it was the pinnacle of browser UI. Everything that came after that (including of course later iterations of Opera, which removed the MDI) has been considerably worse.
For me, it was the pinnacle of browser UI. Everything that came after that (including of course later iterations of Opera, which removed the MDI) has been considerably worse.