When I asked this question using games as the example (hoping it would be more likely to have been done), it was closed as being off topic so let me ask it this way...

Has anyone used a spreadsheet to model a complex, changeable system (something like crowd behaviour, weather systems, a closed ecology, evolution or whatever) and if so, can you point me at it?

I'm hoping for a normal (albeit complex) spreadsheet using the spready's inbuilt formulae and functions rather than something specially coded. I'm also after something where it's possible to change the variables and see the changed outcome - perhaps the variables change using random numbers or the like.