This app allows you to walk around a historic district and have history read to you.
It starts with a *kml file (like GoogleEarth) with GPS info and historic notes. As you walk it figures out how far you are from any historic monument in its data base. When you are within 20 meters of the monument, it reads the description to you.
It comes pre-loaded with data for Brazos County in Texas and White River Junction in Vermont. But new *kml files can be created and dropped in to it.