Stendhal is completely open source. Both client and server are licensed under the GNU General Public License.
You most likely want one of these downloads:
The Stendhal desktop client works on Windows, Mac and Linux. It requires a Java runtime.
If you are a developer, you may be interested in these files. Please have a look at the development corner.
We use Tiled to edit Stendhal maps.
Please see Stendhal Testing, if you want to help us test the next release.
Use this beta version with care as it will contain bugs. Please note: It will not update itself.