labwc is the most mature floating/stacking compositor I know of. It’s roughly designed after Openbox and is configuration-compatible to a certain degree but missing features of it (icons, pipemenus, some window rules etc.).

I recently migrated my main PC to Wayland and there I use Hyprland in “floating mode” (I just set up a windowrulev2 to set all clients to float on the first few workspaces). I’m not happy with it, because Hyprland (of course) lacks everything you expect from a stacking compositor.