Spectrwm is the new name of Scrotwm which has been around for some time.

You need to have dmenu in your path for this (works without it, you'll be noticed that it is
required by spectrwm itself). It must be handled like in i3-wm, which is just install
dmenu in addition to spectrwm.

Works, tested, this message was written from within spectrwm.