Math teachers and students will find helpful resources on GeoGebra, a free and multi-platform mathematics software for all levels of education that joins geometry, algebra, tables, graphing, statistics, and calculus in one easy-to-use package. Users will learn how to create images for paper worksheets and interactive websites with a single click. Educators will also find access to the GeoGebraWiki, a free pool of teaching materials. Any user can contribute and upload material, and all contents of the pool may be used free of charge. http://www.geogebra.org/cms/en
I like this software. It is very useful in class.