GeoGebra is free and multi-platform dynamic mathematics software for all levels of education that joins geometry, algebra, tables, graphing, statistics and calculus in one easy-to-use package. Even better, it’s free! GeoGebra has won loads of awards worldwide.
There are two different versions of Geogebra – a version you can download and run offline, and an online version you can access through your browser.
The Web version can be accessed here : http://www.geogebra.org/webstart/geogebra.html
And the downloadable version can be access here: http://www.geogebra.org/cms/
The GeoGebra site contains quick start guides, video tutorials and some downloadable books, which should help to get you up and running pretty quickly.
GeGebra is a very handy piece of software for maths teachers who want to demonstrate aspects of graphing, charting and geometry and find that their regular IWB software is not enough to do so.