Hi I'm looking for a retro style desktop environment (or maybe just some skin or something) for my Debian workstation. Preferably something that looks like Mac OS 9.
MLVWM is a classic mac window manager for X11
https://github.com/morgant/mlvwm
Also you will need
https://github.com/morgant/mlvwmrc
Also bonus: Mac OS 8 startup for Plymouth
https://github.com/vladkorotnev/System8
Ooh, I wonder how the menu bar works across apps since most are designed to have menus in-window. I remember older versions of KDE used a global menu bar and there were some hacks to move some GTK apps' menus into there as well, but it wasn't totally consistent.
Might have to give this a try.
BTW modern KDE still has this as a module and it works pretty well with both Qt and GTK programs (though with GTK it sometimes shows it in both locations).
The tricky point to your needs is getting the app's menu bar in the top bar. The rest are easy to do with almost all desktop environments. But getting the menu bar on the top bar, I think currently only KDE supports it (with a plugin), and MATE (with another plugin).
However, if you want the general feel of how MacOS 9/X feels, then Gnome with extensions would be your best bet. The rest feel more like simpler Windows, but in a mac skin. Gnome+extensions feel more accurately like a Mac, in terms of overall usability (even if the looks aren't 100% there). So it depends what you're after more: the feeling of using a mac, or the exact looks of it.