Just downloaded the free Spore creature creator module from www.spore.com, and am impressed, to the point of I'll probably buy this game! The shrinkwrapped game allows you to guide a world through 5 stages of evolution:

• Cell Phase
• Creature Phase
• Tribal Phase
• Civilization Phase
• Space Phase
  

The free creature creator gives a taste of the gameplay; I've installed it on two laptops (my kids loved it when I showed them) and am impressed by the design and easy (thus far) gameplay. In keeping with the info focus of this blog, Spore also has some social networking capabilities built-in, allowing players to upload creature designs to youtube. Spore is available on the PC and Mac, as well as other versions for handheld platforms and mobile devices.