Depends on your definition of IDE.  If it is 'big' then afaik, no. 
Nothing cocoa.

Eclipse runs in java and so looks pretty close to native and the 
rubyeclipse plug-in mentioned by Otaku is handy and free, however some 
bits of eclipse do feel a bit non-mac.

If your desire is more limited to text-editor+  then TextMate (39) 
http://macromates.com/ is pretty handy, and appears to have been 
written with ruby and rails top of mind.

If your desire is even more limited, then SubEthaEdit (free for non 
commercial) is very clean - http://www.codingmonkeys.de/subethaedit/

If you want something that will allow you to develop native Mac OS X 
guis, then you can use Mac's XCode together with rubycocoa 
(http://www.fobj.com/rubycocoa/) to draw them.

As an aside, I have occasionally tinkered with the idea of writing a 
'big' native IDE in rubycocoa.  I don't think it would be too hard 
given cocoa's handy toolbox of components.  If anyone is interested in 
collaborating on one, or feels a big need for such a thing, then let me 
know.

Tom

----
Tom Counsell.  http://tom.counsell.org

On 10 Jan 2005, at 00:21, Dr. Scott Steinman wrote:

> I've noticed that a couple of the cross-platform Ruby IDEs can run on
> Mac OS X, but only at a low level (using X11), not natively (with an
> Aqua interface).
>
> Are any native OS X Ruby IDEs available that are being actively
> developed?
>
> Thank you.
>
> Dr. Scott Steinman
> Southern College of Optometry
>