I'm a Mac user too, apparently this is pretty good, uses a port of the underlying software from autostitch.
http://www.kekus.com/download/index.htmlNot used it personally however. I tend just to use Photoshop or Realviz Stitcher.
Not to get too technical, but unless your using a panoramic tripod head (which rotates on the axis of the len's nodal point where the light beams actually converge, rather than using the tripod socket on the base of the camera) you will often find stitching software will struggle where there is objects close to the camera. This is due to parallax.
Thats why you can't make those nifty 360 degree spherical VR panoramas on a normal tripod.
Its kinda difficult to explain, this diagram attempts to show what I'm trying to describe. I've noticed quite a few panoramas on this site with parallax errors, particularly on details like fences. It's also partly responsible for the extreme barrel distortion on some of them too, a result of the software trying to join images which don't overlap properly.
As you rotate the camera, the position of objects in front of the camera will change relative to the background, thus they will not overlap correctly, which is why it won't stitch. If you rotate around the nodal point (located somewhere in the lens) this doesn't happen, and provided you've used the same exposure and focus settings, the images will always stitch, even all the way round a full 360 degrees.
This site has a pretty good guide to avoiding parallax errors in panoramas
http://www.cambridgeincolour.com/tutori ... llax-error