I got into Linux because I can choose everything I want in my computer. Openbox is fast, lightweight, with no bloat, straight to the point.
Openbox basically consists of three files: autostart, menux.xml and rc.xml.
Autostart lists the applications you wish to initiate at startup as easily as adding the command and whatever other arguments you want.
As for menu.xml, it manages the right-click menu in the desktop. There is an application named "obmenu" which does the trick in GUI, so you need not know XML to generate your menu.
Lastly, rc.xml deals with mouse and keybinds, which I consider Openbox's greatest advantage. This was especially useful for me for increasing productivity, since I can do more with less keystrokes, and faster.
I've been using this window manager for three years now (thanks Crunchbang for this), and it works great in low-end machines, since it doesn't eat RAM while running like a full desktop environment such as KDE, Gnome, Unity, Cinnamon or whatever you name.
Great piece of software!

Openbox is perhaps the most famous *box wm, and deservedly so. Even though it is not updated anymore, it's really good as it is, a model for other lightweight window managers.

I hate openbox and your should, too.

Lubuntu inflicts it in an all or nothing way. expand your mind, open minded if you will. Find other WM.

gnome forever... but not lightweight