An unusual genetic engineering simulation video game from Maxis (not entirely unlike their similarly-nebulous but more immediately-grokkable SimLife) where you manipulate variations in speed, strength, stamina, vision and fighting, eating and mating behaviors in artificial life-forms known as Theroids, hand-tuning mutation rates and directing the successful generations against their less-successful brethren.

Like many simulations, very abstract as a 'game', but supportive of hundreds of hours of high-level tinkering, figuring out how to work the engine of these simple creatures.