I had some major problems customizing PlatinumArts Sandbox to my needs, so for the last months I have been playing with the original Cube2 (Sauerbraten), extending the scripting capabilities, and hacking away at the source to make it a bit more rpg-friendly.
I have a short preview of my work on g+ : Plus.google.com
If anyone feel like hacking away at Moonvalley, you are more than welcome, just as long as you keep the project GPL :-)