Wow, I didn't know about RUBE, definitely worth looking at. Even better to see that some interesting Moai-based efforts are on their way !
There is also Level Helper, although it doesn't currently support Moai (however MOAI parser may be very easy to write as there is a Corona SDK export already).
So far, for level design, I use Illustrator or Inkscape to lay out elements, and then add physical properties at SVG Interactivity panel (Illustrator), or SVG Events ( Inkscape ). SVG file format (being XML) is fairly easy to parse, and there are couple of SVG-based level editors such as SVG Level Editor (for Corona) and LevelSVG for Cocos2D.
I have at various times in this forum announced that I'll publish my SVG importer for MOAI here but as in the meantime I have written entire high-level framework from scratch, I'll try to finish the framework, create some samples and tutorials and release everything together.
A quick preview of this functionality:
Actually, these days I am looking for alternative for Illustrator (because of its price and high learning curve) and Inkscape (because its X11 based so I find it extremely user unfriendly on OSX), and was surprised that there is no OSX application in sub $100 range that features a full SVG export. There are a couple of really great vector graphic programs, very affordable (below $25), that would serve as perfect level editors should they supported full SVG export, so I got in touch with developers to see if this could be implemented (as SVG export itself is trivial to code).
Anyway, great to hear more alternatives here, and in the meantime I'll try to improve on SVG-based workflow and post the code to this forum once it's ***finally*** ready