Ruby based spreadsheet on a Mac

I’m toying with the idea of writing a spreadsheet program where the cells can leverage the power of Ruby if need be. I’m going to do this just on the Mac. I don’t care about Windows. I’d prefer to have the user interface use one of the native Mac windows rather than using X11 and XQuartz. So I’m looking for suggestions on how to do the user interface code such as what libraries or methods to use or perhaps those I would want to avoid. I’ve never developed specifically for the Mac so this may be a steep learning curve.