What exactly is the demo and how is it different from an open beta? Well, the demo is a true demo in the classic sense of the word. You can try out cities, but only build them to 22k citizens (the full version of the game lets you create megalopolises of millions of citizens). You'll have access to 3 maps, while the single player mode will give 25 maps on launch, and the MMO Planet Mode will give you 50 maps. This is Monte Cristo's way of opening the game up to all players, considering their unique business model with a single-player and multi-player modes. Check out our previous coverage and their newly-revamped website for more details.
[EDIT: You can now get the demo here.]