You may use GeoGebra free of charge (GNU General Public License).
If you like this program and you would like to support GeoGebra 
in any way, please contact me: Markus.Hohenwarter@sbg.ac.at

Translations
  
Austrian: Markus Hohenwarter (Austria)
Catalan: Jaume Bartrol Brugus (Catalunya)
Chinese: Fu-Kwun Hwang (Taiwan)
Croatian: Sime Suljic and Ela Rac (Croatia)
Danish: Steen Grode (Denmark)
Dutch: Beatrijs Versichel, Ivan De Winne, Pedro Tytgat (Belgium)
English: Markus Hohenwarter (Austria)
French: Pierre Couillard (Canada), 
             Vincent Douce, Nicolas Hainaux, David Tran,
             Noel Lambert, Philippe Pham-Ba-Nien  (France)
German: Markus Hohenwarter (Austria)
Hungarian: Sulik Szabolcs (Hungary)
Italian: Enrico Pontorno and Alessandra Tomasi (Italy)
Portuguese: Humberto Jose Bortolossi (Brazil)
Slovenian: Stanislav Senveter (Slovenia)
Spanish: Liliana Saidon (Argentina)
  
Credits
  * Java symbolic computation library
      Rapael Jolly and Elefterios Stamatogiannakis 
      http://jscl-meditor.sourceforge.net
  * Java EPS Graphics2D package
      Paul Mutton
      http://www.jibble.org/epsgraphics/
  * HotEqn - LaTeX equation viewer
      Christian Schmid
      http://www.atp.rub.de/VCLab/software/HotEqn/HotEqn.html