Where as RPG Maker is Windows focused, MKXP is focused around Linux. This open-source RGSS implementation for Linux was pointed out earlier in the Phoronix Forums.
One of the games to Humble Indie Bundle X, To The Moon, is powered by RPG Maker. Rather than running on Wine for Linux support with RPG Maker, there is MKXP according to Phoronix reader "Ancurio" in our forums.
Also pointed out was Easy RPG, which is an open-source implementation of RPG Maker as well but the older 2000/2003 versions and not RPG Maker XP as targeted by MKXP.
MKXP is able to run games created by Enterbrain's RPG Maker XP natively and without any source-level modifications required. MKXP is licensed under the GNU GPLv2+ license.
MKXP is dependent upon Boost, PhysFS, GLEW, OpenAL, SDL2, and Pixman libraries. It also uses Qt's QMake build system. Those interested in checking out MKXP can stop by its GitHub project page. MKXP is certainly in much better shape than the new GNU RPG Engine.