A new mapmaker package is now available from the download page.
This is the latest release of the public maps, arches, and 0.10.0 test server, and Gridarta.
You should copy your existing unofficial maps and arches somewhere safe before installing this mapmaker. You connect to this local server with the same client you use to connect to the main and test gameservers (see README_FIRST.txt).
For those who build their own server/client and get arches etc. from SVN, and only need to upgrade editor.jar when a new version is available, the latest available pre-built revision number (in this package) is 8557.