Differential (really difference) equations, such as the famous SIR model from epidemiology, can be coded into spreadsheet technologies, but they require some technical expertise, and it can be hard for students to make sense of the model because some columns will end up representing populations while others are constants or changes. VenSim allows a graphical layout that helps separate the kinds of variables at play. Moreover, it allows users to see the impact of changing parameters dynamically, which facilitates the kind of exploration that would be extremely difficult symbolically. It's October, so you might consider adapting SIR to be about a zombie epidemic, asking students to evaluate different plans to fight the scourge.
(Shared by Brian Katz.)