QGIS is a user-friendly Open Source Geographic Information System (GIS) licensed under the GNU General Public License (GPL2). QGIS is an official project of the Open Source Geospatial Foundation (OSGeo). It runs on Linux, FreeBSD, Mac OSX, Windows and Android and supports numerous vector, raster and database formats and functionalities.
Some additional links:
- List of new features
- PyQGIS developer cookbook. PyQGIS can be use for automating QGIS tasks and writing plugins using Python.
- QGIS 2.0 book (from GIS Lounge)