An insidiously addictive simulation game, Zoo Tycoon allows players to create their own zoo, but not just any zoo. It's completely free-form: Start with fences for your exhibits, then pick animals and give them toys, foliage, and anything else you want. For your customers, you can lay down paths to lead them around, then add food stands, amusement rides, even maps and trash cans. Not sure what you need? The zoo advisors will tell you how to make the animals happy, and the customers themselves will tell you what they're looking for, be it snacks, more animals, or anything else. There's also a vast amount of background information on each critter--its diet, its habitat, etc.--which can be useful when you're adding a macrauchenia or a Loch Ness Monster. In all, you can choose over 100 animals, plus countless habitat and park embellishments.