Quantum GIS (QGIS) is a user friendly Open Source Geographic Information
System.  QGIS supports vector, raster, and database formats.
QGIS is licensed under the GNU GPL.
Some of the major features include:
- Support for spatially enabled PostGIS tables
- Support for shapefiles, ArcInfo coverages, Mapinfo and other formats
- Raster support for a large number of formats
- Identify features
- Display attribute tables
- Select features
- GRASS Digitizing
- Feature labeling

WWW: http://www.qgis.org/
