IceWM
IceWM is an X11 window manager coded from scratch in C++. It is relatively lightweight in terms of memory and CPU usage, and comes with themes that allow it to imitate the UI of Windows 95, OS/2, Motif, and other GUI's.
IceVm screenshot (Glamice theme)
IceWM can be configured from plain text files stored in ~/.icewm, making it easy to copy settings. IceWM has an optional, built-in task bar with menu, tasks display, network and CPU meters, mail check and configurable clock. IceWM catches alt-ctrl-del by default. Official support for GNOME and KDE menus are available as a separate package. External graphical programs for editing configuration and menu exist.
Displaying icons on the desktop requires external programs. Unlike KDE and GNOME, IceWM does not contain an automounter. Starting to use IceWM requires writing a ~/.Xclients or ~/.xsession manually.