tcsysmon is a dock app that monitors Mem/Swap/DiskIO/Uptime and displays blinky lights for your interrupts and page in/outs. Its goal is to display as many real-time system statistics as possible with a minimum of CPU usage. It includes MMX routines for faster updates on newer CPUs.
The Virtual Tab Window Manager (VTWM) is a virtual window manager with adjustable graphical complexity. With minimal settings, it is ideal for limited resource situations, using little memory, little CPU time, few colors, and little bandwidth. Fully blown, it supports m4 and regex processing of the resource file, sound effects, user-defined color icons and buttons, and more.
Window Maker is an X11 window manager designed to give additional integration support to the GNUstep Desktop Environment. In every way possible, it reproduces the elegant look and feel of the NeXTSTEP[tm] GUI. It is fast, feature rich, easy to configure, and easy to use. In addition, Window Maker works with GNOME and KDE, making it one of the most useful and universal window managers available.