> Gimp for a looooong time was a multi-window user interface, completely antithetical to almost any other application released in the last 20 years or so.

Same as Mac software in the late 90s. GIMP is/allows MDI, tabs or whatever it is called. A decade old at least, Wikipedia is not clear if the change was "new feature" or "new default but avaliable before". Maybe Mac native software went that way too, no idea what is the trend there now. Most things reinvent everything including window management, poorly, inside a browser, anyway.