IceWM

Lightweight window manager for the X Window System, which provides full-fledged control via keyboard shortcuts, the ability to use virtual desktops, taskbar and menu applications. 

The window manager is configured through a fairly simple configuration file, it is possible to use themes. Built-in applets are available for monitoring CPU, memory, and traffic. 

Several third-party GUIs for customization, desktop implementations and menu editors are being developed separately. The code is written in C++ and distributed under the GPLv2 license.