Fvwm-mode is a major mode for editing FVWM configuration files.
- syntax hilighting
- execution of FVWM commands from Emacs
- insertion of templates for various constructs
The latest stable and development versions can always be found here along with a manual.
There’s an (older) alternative mode at http://www.cs.virginia.edu/~wh5a/personal/Emacs/fvwm-mode.el.