ImageFuser is a graphical frontend for the open source command line tools Enfuse and Align_Image_Stack.
Next to these tools Phil Harvey's ExifTool is used to copy exif, jfif, tiff, iptc, gps, icc profile data etc. to the new images.
ImageFuser is GPL Open Source software. It's free to use for as long as you wish and 100% functional, but if you like it and continue to use it, a donation is appreciated. ImageFuser is written in AppleScript Studio as a Universal application. It should work on any Mac running Tiger (10.4) or newer.
Enfuse is written by Andrew Mihal (main developer) and released as open source. Align_Image_Stack is one of the "helper" tools that come with Hugin (main developer Pablo d'Angelo).