LiquiData [liquidata.org], developed by several students of the University of Applied Sciences Potsdam, is an application for a multitouch table which reveals one's movement data through a city on a map, as captured by a smartphone.
The gathered data from the last trip through the city is visually "poured out" on a map and makes the paths and places visible while all unvisited places stay covered by a semi transparent dark "fog". If 2 people each put their phone on the table simultaneously, then both their paths are shown, and any overlappings are shown. The idea here is that these persons then can discover what places they both visited and liked.
By way of interacting with the smartphone, the map can then be enriched with photos and comments to create, for instance, a shared, interactive map located in a hotel lobby that collects interesting walks, restaurants or shops.
Watch the documentary movie below.