ElectricSheep.Org

First created in 1999 by Scott Draves and updated continuously since, the Electric Sheep is a form of artificial life, software that recreates the biological phenomena of evolution and reproduction though mathematics. The system is made up of man and machine, a cyborg mind with 450,000 participant computers and people all over the Internet.
This is a distributed system, with all participating computers working together to form a supercomputer that renders animations, called "sheep", that everyone sees. The human participants guide the survival of the fittest by voting for their favorite animations.
Each participating computer follows mathematical instructions, Draves' Flame algorithm, to render its own piece of the larger work. The images are sent back to a central server which compresses them into animations which are sent back out to the viewers. The website shows the family tree for each sheep, including its parents and offspring, and viewers can track family resemblance.
Between the server, and clients for all OSes, the system is comprised of about 150,000 lines of code. The code is open source, which has allowed it to benefit from contributions from many programmers.