http://www.godotengine.org/wp/

This is legitimately amazing.

Why? Because it has the capacity to make 3D tile-based games (somewhat similar to Gen VI) and is open-source with code already available for Mac OSX and Linux. If we had someone who could model stuff, we wouldn't necessarily have to fiddle with RMXP's quirkiness, plus since we have code access, we could technically turn it into a Pokémon engine off the bat.