Stop Disasters Game

I'm starting to get taken by online games that I can see have a genuine educative purpose. Electrocity has me captivated.

This is a new one to me. It has five different disaster scenarios and a time limit before disaster strikes. You have a budget and have to prepare the location for the coming disaster. This would fit well into any disaster unit at the upper end of primary or lower high school level.

If you can recommend any games like these two I'd love to hear from you. As always I'm a cheap skate so I want free, preferably online suggestions and they have to be educationally useful. I'm sorry but Wolfenstein just doesn't do it for me.