OpenBox is a light , stable and fast X window manager for X desktop environments.  and also it is default window manager for LXDE desktop environment. if you want to change Linux Mint 13 Mate window manager to OpenBox follow these steps:

  1. Install "openbox" package from package manager.
  2. In a terminal type "mateconf-editor"
  3. In configuration editor tree go to "/desktop/mate/session/required_components/windowmanager" and replace "marco" with "openbox".
  4. Open Startup Applications from mint menu, and add a new startup program "OpenBox" with command "openbox --replace".
  5. now restart your machine.
  6. in your first login you may face a session error dialogue, click on the "ok" button in the dialogue and then in the login page change your session to "mate"
  7. after login you can go to the "Openbox Configuration Manager" program for further configuration.
now you have OpenBox window manager with Mate desktop environment.

have a nice time.