Under X11 there is Openbox, bspwm, herbstluftwm, dwm, i3, Awesome, Ratpoison, spectrwm, Qtile, …
Under Wayland: Weston, LabWC, Wayfire, Sway, River, Cagebreak, dwl, …
I keep things pretty dull and use Openbox + LXQt. It is a stacking WM that is stable, and LXQt is snappy.
If you are looking for a light DE LXQt is very light, Plasma is lighter than it used to be, but it also has loads of features. Xfce has more options for configuration than LXQt and I think it isn’t quite ready for Wayland.