xlockmore is an enhanced version of xlock. It incorporates several new commandline options, which allow you to run it in a window, in the root window, in a different size/location, change the size of the iconified window, to install a new colormap and delay locking for use with xautolock.
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.
BitLife is an implementation of life using boolean operations (AND, OR, XOR), computing each new cell from 9 bits (itself & neighbours). It's performed in parallel on the whole image by bitblit operations (with hardware accelearation where possible). This also allows many parallel life games to run in each bitplane of the screen, giving a translucent blending effect. A proof-of-concept Python (pygame/Numeric) implementation and an xscreensaver hack are included.
GNUSTEP Live CD contains a lot of software for GNUstep, a free implementation of the OPENSTEP framework (which is also directly used in Mac OS X as Cocoa). It includes excellent applications for RAD (GORM and ProjectCenter). The CD is available for i486, AMD64, Apple Mac PowerPC, and Sun UltraSPARC computers.