A couple of days ago I came across the teaser site for Spore, the next game by Will Wright, the fella who brought us Sim City.
In Spore, you are responsible for evolving the life on your planet, from the level of denizen-of-the-primordial-soup all the way up to galactic overlord.
Clicking on the egg brought up a creature editor, and allowed the player to “evolve” with a new generation of critters. The editor was amazingly flexible. Wright could give his creature extra vertebrae, he could give it fins or tails to move faster, he could add claws or extra mouths, whatever he wanted. More importantly, all the creature animations weren’t hard-coded; they were dynamic. If he put six tails on his creature, the game would figure out how a six-tailed creature would move. The critter was completely his.
Supposedly the game will be out in 2006.