This is the no-frills window manager, it is fast and stable.
With twm, you have the option to configure or customise the menus in your window manager. Copy the file system.twmrc in /usr/local/X11/lib/X11/twm/ into your home directory as .twmrc and edit it.
You can do this by typing:
% cp /usr/local/X11/lib/X11/twm/system.twmrc /.twmrc
And then you can edit your .twmrc file from your home directory.