What do you call a fish with no eyes? fsh!
Fsh was created because I wanted fish on my desktop. I have a coworker running Linux, and there's a feature (google freethefish) that lets you have a fish swimming around on your desktop. I'm running Windows, so obviously, if I wanted a fish, I was going to have to do it myself.
Since then, fsh has added a number of features. You can have basic fsh, ninja fsh, invisible ninja fsh, sharks and barracuda. Sharks will eat anything except other sharks, while barracuda will eat basic and ninja fsh. Ninja fsh take the fight to the predators, and actively hunt down sharks and barracuda.
You can customize how many of each fsh you get, along with a number of other parameters (like whether predators eat or just kill, whether to show blood on kills, etc) using the fshConfig program.