I agree this question is vague in terms of your requirements. Are you
wanting to generate some tables? Or something more complex? Do you
want to output to HTML, PDF or an image? Am I correct in thinking that
you mean something along the lines of winforms rather than webforms
when you say "Ruby GUI"? If HTML is not an option, your choices will
be severely limited.
One of my current projects generates a report with text, tables and
charts. The client also required that it be generated as a PDF _and_
be available as HTML. I wanted to use the same views for both, which
meant many of the usual tools were not an option. I found Prince
http://www.princexml.com/ and have been thrilled with it. The basic
concept is HTML + CSS = PDF. With columns, fonts, etc., the final
output is quite professional.
The software is not free -- in fact, the license is a bit steep -- but
you can try it for free. There's also a site that resells the software
with the SAAS model
http://docraptor.com -- I haven't tried it, but it
looks like a good option.
jw