QGIS (previously known as Quantum GIS) is a cross-platform free and open-source desktop geographic information system (GIS) application that supports viewing, editing, and analysis of geospatial data.
It is software for power-users with hundreds of useful plugins, but is accessible to beginners for many useful things - such as opening geodata formats like KML/KMZ files, browsing WMS services or OpenLayers.
This screenshot of QGIS is from a School of Data introducory module which uses the OpenLayers plugin. Visit QGIS.org for more information on getting started.
• Recommended by: Oleg Lavrovsky