Despite the acronym, Creatures DS has nothing to do with Nintendo's latest handheld. It actually stands for Docking Station.
A stand-alone-demo/addon for Creatures 3, DS is an artificial life simulation where you raise a group of small furry creatures called Norns. You need to teach them how to speak and how to survive, and they will in turn pass this information on to their friends and families. Although you only get one breed of Norns in DS (so they'll all look the same), you can get another official pack from the same site for free, and there are a great many fanmade breeds you can download to add some variety to your world.
Best of all, DS is fully online- it has built in chat, and you can create portals to send Norns between worlds to trade Norns with your friends. It's a truly global community!
DS can be downloaded completely free from here- www.gamewaredevelopment.co.uk