Haiku made them magnetic. In classic BeOS you had to manually position the windows on top of each other, then hold shift and manually drag the tab over from the left. And they wouldn't be tethered together: moving one window wouldn't move the other. It was annoying enough that I never bothered. By the end of BeOS's life I was mostly using the Mac OS 8 titlebar style (accessed by holding down all the modifier keys and pressing the Be menu).
reply> I haven't seen anything like it
replyI remember using the fluxbox wm like this back on the university Sun machines
Yep, reeeally nice feature, used it on Linux. After that I wondered why apps bothered to implement their own tabbing when you could just stack Windows as tabs (assuming more WMs would adopt that feature).
replyAlso Windows was going to have this, but never left the preview builds, there was a BUILD or Ignite session were it was demoed.
replyGranted it was already Windows 10, so nothing that original.
It would just stack the windows of different sizes, so if you hit the Winamp tab the smaller Winamp tab would be at the top of the stack. Pretty simple and intuitive.
replyI loved the tabs on BeOS.