Using KDE here, but there might be a solution that works with other desktops environments too. I often am dealing with many many windows. Most windows contain many tabs (e.g. a Dolphin window with many tabs, or Firefox, Konsole, etc). The window title will change based on my current tab (which for the most part is helpful most of the time), but when working with so many windows I'd like to organize them a bit and be able to manually re-name the window, overriding the the window title that the application gives. I might name one Firefox window "Research" and other Firefox window "Documentation" to be able to easily distinguish between the windows that I've used to organize and group different tabs accordingly.
Ideally I'd be able to click on a window title bar and easily give it a custom name, but I'd settle for a solution that's slightly more cumbersome as long as it works.
wmctrl -r :SELECT: -T "Research" but that only works temporarily (the title is reverted when the application changes it, for example when switching tabs).