Afaik the Win3 file dialog gets called up by some old apps that use old APIs. I think I even ran into it in Wine. The analog in Unix apps are GTK's file dialog

Afaik the Win3 file dialog gets called up by some old apps that use old APIs. I think I even ran into it in Wine. The analog in Unix apps are GTK's file dialogs, which always look jarring and out-of-place anywhere other than Gnome (and maybe XFCE and KDE, dunno)—making me feel like I stepped into 90s Unix with those Motif-derived concrete slabs. Plus they're un-integrated with non-Linux OSes, missing features. And the dialogs keep being dragged around by GTK apps—open Gimp on Mac or Windows and there you go: GTK dialogs.