MapTube is a website for sharing maps which are displayed using either Google Maps or Open Layers.
The main principle of MapTube is that shared maps can be overlayed to compare data visually. For example, to see a map of the London Underground overlayed on top of a map of population, go to the search page and enter the keywords "tube" and "population". Then click on the two relevant maps to add them. They will be displayed when you click on "View". The resulting map can then be linked to on a web page as follows:
In this example you can see how areas of high population density in London follow the tube network and where there are areas of low population density in the Lee valley to the North East.