Toolkits for 2D Animation?

profBill asks: "I work in the area of complex adaptive systems, that is understanding the emergence of complexity from the interactions of many elements (immune systems, economies, ecosystems, etc.). In particular we are using evolutionary computation to create elements/creatures that can co-exist in an ecosystem with certain interactions and relationships. All that is very interesting, but in the end, assuming we create such creatures, I have to show them to the ecologists and biologists so they can understand what is going on. The only way I can imagine doing it easily, other than with graphs and charts, is to create a 2D animation of the creatures and their interactions that these folks can watch. My problem is that there are so many choices for a toolkit to build such a 2D animation. My goal is not a movie of ILM quality, but something 'good enough'."

"'Good enough' for me means:

• Quick and dirty, that I can tune as needed.
• Zoom capability on a grid
• Pop up menus on any one grid element to get information.
• Scrolling, resizing, the typical.
• Be able to hook to a C/C++ program to get a creature's behavior

What would you use to build such an animation?"