Quantum GIS (QGIS) is a powerful and user friendly Open Source Geographic Information System (GIS) that runs on Linux, Unix, Mac OSX, Windows and Android. QGIS supports vector, raster, and database formats. QGIS is licensed under the GNU Public License.
Screenshot of Quantum GIS development version 1.5.0
The name Quantum GIS really has no siginificance, other than it starts with a Q and QGIS uses the excellent Qt Toolkit from Nokia (formerly trolltech).
A Brief History
The Quantum GIS project was officially born in May of 2002 when coding began. The idea was conceived in February 2002 when Gary Sherman began looking for a GIS viewer for Linux that was fast and supported a wide range of data stores. That, coupled with an interest in coding a GIS application led to the creation of the project. In the beginning Quantum GIS was established as a project on SourceForge in June 2002. The first code was checked into CVS on SourceForge on Saturday July 6, 2002, and the first, mostly non-functioning release came on July 19, 2002. The first release supported only PostGIS layers.
QGIS Release Timeline