QGIS is a user friendly Open Source Geographic Information System (GIS) licensed under the GNU General Public License. QGIS is an official project of the Open Source Geospatial Foundation (OSGeo). It runs on Linux, Unix, Mac OSX, Windows and Android and supports numerous vector, raster, and database formats and functionalities.
Popular alternatives to QGIS include GRASS GIS, another free and open source system similar in scope and ArcGIS, the most commonly used proprietary GIS software.
Open Street Map is a project that creates and distributes free geographic data for the world. The project is collaborative, rely on volunteers providing GIS data. The data is freely available for download and use in GIS software.