Favored Freeware: Fish

Fish is an aquarium simulator. It allows you to add fish to an underwater environment and customize them. Fish show complex behavior. You can feed them, see their evolution as they grow, use different cameras to track them, and save different aquariums for later use. Fish can also be shared with others over a local network.

Pros: Fish will provide you with hours of serene fish-related enjoyment. It is a powerful, intelligent, and fun aquarium simulator. Once you install Fish, add a few random fish (or select your own), and activate the Full Screen mode, you will never again have to worry about buying expensive fish food and aquarium maintenance supplies.

Cons: Unfortunately, Fish is not available as a screen saver.