Open RPG Maker is a free and open source clone of features from the RPG Maker series (i.e. rpgmaker200, rpgmaker2003, rpgmakerxp), as well as many other features. All of the data files are in XML format and are easily editable with any text editor.
I've been trying it out, just started, so take what I say with a grain of salt. However, apart from being able to run the game (which you guys are already working on), it would be nice if when the game can actually be made (or compiled) we can see the source-code of the game, and even edit it (sort of like Kompozer, but instead of webpages, it's an RPG). Other than that, I think this is well on its way to being a great game maker for both Linux and Windows.