Geometry Playground is a free ruler and compass Java application for multiple geometries. (You will need Java 1.50 or greater to run it.) Positive comments and praise should be sent to Daniel (deej) Heath. Complaints, criticism, flames and bug reports should be sent to Joshua Jacobs. You will need to replace the -A.T- in either email address with the "at" symbol (sorry for the inconvenience -- this protects us from spam). To start Geometry Playground, follow the link below.
Although most features of Geometry Playground are self-explanatory, there are some short tutorial videos that might help you get started. They are:
There is an editable wiki, which includes hands-on discovery activities. Do you want activities for your geometry class? Find some at the wiki. Do you want to make adjustments or additions to the curricula? Do so at the wiki. The code is also open source, so that you can add to or edit that as well. Contact Josh if you wish to do so. There are some constructions saved in a .zip file, including some traditional Euclidean constructions and their counterparts in other geometries. Follow this link to download those constructions.
Do you want Geometry Playground to be offered in your language? Download Playground Messages, translate it, and send it to deej. Note that "(your language)" should be translated into the word for your language in your language. For example, in English, that line reads: "languageText = English".
Arguments can be passed to Geometry Playground through the jnlp file, as showcased in file PlaygroundExample.jnlp.