OSGeo4W includes open source GIS desktop applications (QGIS, GRASS GIS), geospatial libraries (PROJ, GDAL/OGR, GEOS, SpatiaLite, SAGA GIS), scripting languages (Python) as well as many other geospatial related packages.
The OSGeo4W installer bundles relevant OSGeo software packages plus additional requirements into a convenient MS Windows based installer. Re-running the installer will update existing packages and/or permit to modify the installation.
The Express install is a quick way of installing some of the most high profile OSGeo4W packages in a minimum number of steps. The Advanced install allows control over many details of the installation such as where to install, use of proxies, and local cache directory selection.
Easy testing of daily QGIS and GRASS GIS development builds on MS windows operating systems is one of the highlights of OSGeo4W.
OSGeo4W is a joint voluntary community effort under the umbrella of the Open Source Geospatial Foundation. Contributions for maintaining the environment are welcome.