xscreensaver will run several programs to continuously update the
screen instead of going blank.  You can specify the programs and their 
arguments using resources.

Xscreensaver will make use of any installed OpenGL libraries, such as
Mesa (also in the ports collection).

It doesn't work very well with my XF86_S3 with the MIT-SCREEN-SAVER
extension, so it is disabled in config.h.  It makes very little
difference anyway as the saver still watches the keyboard and mouse
activity.

http://www.jwz.org/xscreensaver/

-Satoshi
asami@cs.berkeley.edu