tested on openbsd 6.4
cwm(1) is my favorite window manager for x11. it has a tiling mode, so i don't have to rearrange windows manually.
cwm(1) is in openbsd base.
$ echo 'exec cwm' >> ~/.xsession
here is my .cwmrc. quite often i keep just two windows open. on the left side: tmux in xterm(1). on the right side: firefox.