Comment by citrin_ru
11 hours ago
IMHO peak GUI was in 2000s - on Windows most app used Win32 API and apps which followed "Microsoft Windows User Experience" guide had consistent UI/UX. Since then Microsoft introduced many competing frameworks to create GUI all look slightly different and UX is less consistent too. And then Electron come which brought inconsistency of web to the desktop apps.
That is very rose-tinted view of the era. In reality in early 00s lots of software had their own wacky UI toolkits. MS Office is of course the most notable example, but also iirc all of Adobe/Macromedia or every 3d modeling (Lightwave, Maya etc) and audio production software. In the enterprise realm people were doing Java AWT (and later Swing) UIs. And then there were the classics like WinAmp with its iconic theme support, or Mozilla with XUL (and themes).