Mac Installer Package for both OS X Mavericks (10.9), Mountain Lion (10.8) and Lion (10.7).
This version requires separate installation of dependency framework (GDAL Complete) , also found at the download link below.
For many flavors of GNU/Linux binary packages (rpm and deb) or software repositories (to add to your installation manager) are available. Please select your choice of distro below:
More specific instructions about downloading QGIS stable vs QGIS development can be found in All downloads.
For testing and learning purposes, a sample dataset is available, which contains collections of data from different sources and in different formats.
QGIS is open source software available under the terms of the GNU General Public License meaning that its source code can be downloaded through tarballs or the git repository.
QGIS Source Code is available here
Refer to the INSTALL guide on how to compile QGIS from source for the different platforms: here
Plugins for QGIS are also available here.