Joe[he]#039[/he]s Window Manager (JWM for short) is a lightweight window manager for X11. It[he]#039[/he]s written in C, minimally using Xlib. Because it[he]#039[/he]s so small and simple, JWM makes a great window manager for slow or old computers. The Raspberry Pi barely registers that JWM is running, leaving precious system resources for more important tasks than the desktop.

Source: LXer – Revamp your old Linux desktop with Joes Window Manager