fvwm1 software package provides Old version of the F(?) Virtual Window Manager, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install fvwm1
fvwm1 is installed in your system.
Make ensure the fvwm1 package were installed using the commands given below,
$ sudo dpkg-query -l | grep fvwm1 *
You will get with fvwm1 package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | X Window System software |
| Package | fvwm1 |
| Version | 1.24r-56 |
| Description | Old version of the F(?) Virtual Window Manager |
| Sub Section | x11 |