Rabbits are blue, foxes red
One of those catchphrases about educational software is that it can show things or model ideas that you can't handle any other way. But, while you can find software that simulates science, few titles come as close to Creatures in providing a model you can really get to grips with. That it's not multimedia, nor on CD-Rom, nor in need of the latest computer, will be a selling point to all but the bloodthirsty.
Creatures shows a population of rabbits as blue blobs on the screen. Here, too, are green blobs or grass. A click then shows the blobs appearing and disappearing as they live and die over many generations. You can stop this, add a few foxes or red blobs and watch them cull the blue rabbits. More than this, a window indicates the number of organisms on a rolling time graph.
This nicely shows the expected pattern where more foxes leads to fewer rabbits, which leads to fewer foxes and more rabbits. That the pupils have to re-scale the graph as this goes on makes a good point about axes. It's easy to print these graphs, or to copy them to your word processor to write an enjoyable worksheet.
So much for the basics. A suitably brief booklet explains how you can use it to show an idea like "pyramids of numbers". Also, by moving sliders to change the sunlight, grass and fox death rate you can see how one end of a food chain effects the other. You can throw a few disasters at the system, too - an asteroid dust cloud, a disease in the rabbits or over-hunting of foxes.
But rather than rabbit on, I think science teachers will find here a learning tool that fits a demo, a lesson or whatever time slot they are happy parting with.