Well, I tried Shoes, Titanium, and RubyFX (or was it FXRuby?) and am not yet quite happy with the stability and cross-platform support from any of them as desktop application GUI tools. Next in line is Adobe AIR. Anyone know what the best tool is that will integrate Ruby and Adobe AIR? Is it even possible?
I think the better question might have been "is there an AIR/Ruby integration framework?" because I don't recall ever having seen such a thing...
Did you consider Google as a possible first port-of-call? ;-)
First result I got was some info at RubyInside.
However, the fact that this question is (as I write this) the #8 search result suggests that there may may not be much to find.
Beyond that, I'd also suggest taking a look at WxRuby, which seems - from a Windows-only perspective so far - to produce nicely native-looking UIs.
Have you considered using jRuby and Swing? Using Ruby really makes Swing much more pleasant to work with.
It appears that at the time of writing, there are no Ruby/AIR frameworks.
I'd agree that there isn't a framework that answers your question, per se. But if you have a majority your rails stuff written, a good 'service wrapper' that you might want to look at is weborb. We use it for our C# classes and it's only about 10Bil times faster than flat xml service calls (You'll still receive xml, but it will be serialized/deserialized --- may the FSM bless AMF.)
True, you'd still have to write a UI, which, by the wording of your question, I'm guessing you wanted to avoid.
Is this the sort of thing you are looking for? http://www.appcelerator.com/products/titanium-desktop/