Softwares

1. Sage is a free open-source mathematics software system licensed under the GPL. It combines the power of many existing open-source packages into a common Python-based interface. It is a free open source alternative to Magma, Maple, Mathematica and Matlab.It can be downloaded through http://www.sagemath.org/.

2. Texmaker is a free, modern and cross-platform LaTeX editor for linux, macosx and windows systems that integrates many tools needed to develop documents with LaTeX, in just one application. Texmaker includes unicode support, spell checking, auto-completion, code folding and a built-in pdf viewer with synctex support and continuous view mode. Texmaker is released under the GPL license . It can be downloaded through the site http://www.xm1math.net/texmaker/.

3.  Other important free open source software can be downloaded through the following sites 

http://www.damicon.com/resources/opensoftware.html

http://www.tripwiremagazine.com/2010/03/20-most-popular-open-source-software-ever-2.html