At the IBBT iMinds conference last week, I met Dirk Frigne, the lead of the geomajas open source project.
At first sight this is google maps on steroids. If you look at the examples they can do some amazing things.
However, the potential is a lot bigger. This is not just about geographic data and maps. This can be used for a lot more. You can use this for any kind of 2D data which can be enhanced and made interactive. Instead of a country or street map, you could put this on a building plan or advanced graphs or visualizations. Really cool and worth investigating.