QGIS is a professional GIS application that is built on top of and proud to be itself Free and Open Source Software (FOSS).

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.

http://qgis.osgeo.org