With MappiMundi you can easily create/explore maps on steroids. With these maps, your users can travel through time and choose what layers of data to display.
For example, you could explore the whole World War II on an interactive map, create your own travel map, or create a map to cover in live some big in your area.
It is free for everyone and does not require technical skills.
The idea of the app is awesome, although it can benefit from a few improvements..