Hi Obinna, Which open source GIS software do you want to download?

You can download ILWIS via link below:

http://www.itc.nl/ilwis/downloads/ilwis33.asp

http://www.itc.nl/ilwis/downloads/ilwis33.asp

You can download QGIS via link below

http://www.qgis.org/en/site/forusers/download.html

http://www.qgis.org/en/site/forusers/download.html

QGIS should be the most powerful at the moment in terms of functionality and format support. If features many of the tools from GRASS and SAGA as well.

http://www.qgis.org/en/site/forusers/download.html

If you are working much with raster data and landscape analysis SAGA might be the tool of your choice. The functionality of the standalone installation exceeds the SAGA tools provided within QGIS.

http://www.saga-gis.org

If you generally have trouble installing software (drivers, dependencies, permissions) I can highly recommend Whitebox GAT. It is JAVA-based and runs without installation.

http://www.uoguelph.ca/~hydrogeo/Whitebox

Please see attached PDF file for many open source options

http://www.gvsig.com/es/productos/gvsig-desktop/descargas

http://www.qgis.org/en/site/forusers/download.html

http://www.openjump.org/

http://www.dpi.inpe.br/spring/english/download.php

http://www.opensig.es/index.php?option=com_docman&Itemid=42

Many thanks....Ceaser 

Probably the best open source GIS software's today (with fast learning curve) are qGIS as a complete solution and SAGA GIS for landscape analyses with more than 100 modules. However, SAGA lack the final output map design and the latest qGIS version is near the productivity of ArcGIS. So if you need detailed analyses go for SAGA, and if you like good final maps, download qGIS (or you can combine both).

Here are one the top 15 best free GIS software available including QGIS, GRASS GIS,WHITEBOX GEOSPATIAL ANALYSIS TOOLS and more,

The link to download software and related materials are also included. Read the following website 

http://monde-geospatial.com/15-amazing-free-gis-software/