This idea to combine Xfce with Fvwm I found in Linux Questions discussions. An old topic (2008), a common practice in the mid-20s to merge WMs. Xfce is an excellent application manager and by merging it with the best window/virtual manager Fvwm, the result is light with unlimited functionalities.
This is how it looks:
Xfce panel 1 (taskbar), panel 2 (app icons), and whisker menu. Visible Fvwm extensions (left to right):
Fvwm OverView button of current windows.
Menu for system tasks and wallpapers.
Thin window title bar.
Window manager bar to resize, move, tiling, etc.
CurW/AllW - List of windows on current and all desk pages.
VM Desk - Virtual Window Manager 2x2 Pages.
Thumbnails of iconified windows (terminal and thunar).
1x5 Miniature view of desktops.
Calendar, time, and date button.
Install Xfce and Fvwm (2 or 3), and download Xfce-FvwmEXT package (one install and upgrade with Extension Installer): SourceForge GitHub
Extract and copy subfolders to ~/.fvwm
Copy ~/.fvwm/setup/autostart/XfceFvwm.desktop to .config/autostart/
or add this file and content to .config/autostart/XfceFvwm.desktop
If remember, the default menu in Fvwm1 had this option. Does it require a specific package to work?
It works ok but @Mjaakko was asking on MX Linux because it doesn’t work on all installs. Something is missing.
I think there is a misunderstanding, you do not merge window managers, there can only be one of those, you replace the other window manager. Xfce is not a window manager, it is a desktop environment which contains a window manager and other pieces. When you --replace the xfce window manager with fvwm, you are running fvwm instead of xfce’s window manager. But the other pieces of software (panels, file managers, etc) will stick around.
Better alternatives are to (a) tell the xfce session to just run fvwm directly as its window manager (I’m unsure if this is still possible) instead of its own, or (b) from inside of fvwm’s StartFunction run the non-window manger pieces of xfce you want to include in your setup.
In the case of openbox (being mostly a wm) it won’t contain a lot of the other pieces, so you will probably replace almost everything, and it would be better to just launch fvwm directly.