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.
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.