I'm currently creating a free, open source RPG builder that will be cross platform and support many cool features, including an action/rhythm battle system which you can test out here: http://www.newgrounds.com/portal/view/616768! The builder will have an accessible dual-scripting system and be highly expandable, including a powerful plugin API. The editing capabilities are inspired by RPG Maker and based off of an older tilemap editor I have been developing on and off in my free time for the past year or so. The builder also uses the great 16-bit style graphics provided by the Liberated Pixel Cup/Open Game Art.
I know first hand how hard finishing a project like this can be. I've had experience making game development tools before including VIDE, a 2D animation tool, HTML Tactics, a DOM-based tactics game editor, and a 3d cloud and atmosphere rendering API. I'm also the founder and lead programmer of Fancy Fish Games, with 6 games released so far. I feel I have the skills to make this project a reality as well as the knowledge of what it's like to be a game developer using the tools! With my experience and a large codebase already complete, I am confident I will be able to come though and finish this project, but I'm going to need a little help!
A 2x speed example video of me creating a simple house interior in the Rhythos Map Editor.
That's why I've started a kickstarter page (which includes a lot more details about the project) here: http://www.kickstarter.com/projects/davidmaletz/rhythos-rpg-builder! If you're able to back the project, that's great! But even if you can't contribute monetarily, feel free to contact me if you are interested in supporting the project as a coder or artist! This is truly a community-driven project and any support possible (even just spreading the word to other developers) would be awesome! You can also peruse the current codebase on github here: https://github.com/davidmaletz/rhythos . It still needs integration work and a lot of features before I'll consider it stable, but feel free to check it out and let me know if you are interesting in contributing code!
And of course, let me know if you have any questions, comments, or feature requests - this project is very expandable, and I hope to support a lot of options, features, battle systems and release targets eventually. I'm creating this tool for the community and with the community, so I want to know what you want!