Here you can find some useful maths software and tools. It's all open source or freeware, so feel free to download and use.
MiKTeX is a free mathematical typesetting software, based on LaTeX. It has more powerful functions than any word processor, but lacks a WYSIWYG interface, so it takes some time getting used to working with it.
R is a free software for statistical computing, and S-PLUS compatible. It provides powerful capabilities for data mining and analytics, as well as easy to use charting tools.
GAP, short for "Groups, Algorithms and Programming", is a free system for computational discrete algebra, and helpful for abstract calculations in many areas of group theory.
Very nice fractal generator, the oldest and best of its kind. Fractint was first published in 1988, and provides a massive variety of functions and options.