The best replacement for openbox is fluxbox.

The best alternatives to openbox are rated as following:
★★★★★  fluxbox
★★★★  xfce
★★  lxde
★★  blackbox
★★  enlightenment
★  awesome
★  i3wm
★  xmonad
★  gnome 3
★  kde
★  metacity
★  gnome
★  jwm
★  dwm
★  fvwm
  dreambox
  skybox
  xfce4
  compiz
  windowmaker
  icewm

Your alternative for openbox is not listed? Suggest!
Speaking about openbox, one probably shouldn't forget about gnome.

Other search terms related to openbox and their ratings are:
★★★★★ gnome
★★★★★ kde
★★★★★ compiz
★★★★ xfce
★★★ tint2
★★★ awesome
★ ubuntu
★ gnome 3
★ lxde
★ xcompmgr
gdm
pypanel
You have in mind a companion for openbox and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of openbox in all years. Click on graph for more.
openbox
fluxbox
xfce