Callisto 1.1 for Mac can be downloaded from our website for free. The program lies within Design & Photo Tools, more precisely Viewers & Editors.
From the developer:
Callisto is a plug-in for Adobe Photoshop that allows you to create terrains and spheroidal objects ("planets"), and also import and render 3DMF models (3D models conforming to Apple's Quickdraw 3D standard).
You may want to check out more Mac applications, such as Io Lander X, which might be similar to Callisto.