Download of Portable Gimp.app 2.2 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application lies within Design & Photo Tools, more precisely Viewers & Editors. This free Mac application was originally developed by Carlo Gandolfi. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
Portable Gimp.app is the Gimp.app self-contained application bundle of the GNU Image Manipulation Program for OS X by Aaron Voisine packaged as portable application so you can carry around with you on any portable device, USB thumb drive, iPod, portable hard drive, memory card, or other portable device (also on your internal hard disk) as long as it has 190 MB of free space and use on any Mac OS X computer, taking your preferences with you.
You may want to check out more software for Mac, such as Gimp, App for Vine - Pro - Menu Tab or Nox App Player, which might be similar to Portable Gimp.app.