Allin1 is a little dock applet for FluxBox and similar window managers. It monitors CPU load with a moving graph, memory and swap usage with histograms, battery and power status with histogram and icons, ethernet/PPP interfaces with icons and histograms (linear or logaritmic), filesystem space, and Seti@home progress.
KNOPPIX is a bootable CD with a collection of GNU/Linux software, automatic hardware detection, and support for many graphics cards, sound cards, SCSI devices, and other peripherals. It can be used as a Linux demo, educational CD, rescue system, etc. It is not necessary to install anything on a hard disk due to on-the-fly decompression.
Sherman's aquarium is a screen saver, a GNOME panel applet, and a dock applet that provides an aquarium with fish and/or turtles. In applet mode, it can display lots of information, such as CPU load, temperatures, memory usage, and many other things. Both the applet and the screensaver are very configurable.