Downloading PowerMask 1.0 for Mac from our website was free. The application lies within Design & Photo Tools, more precisely Viewers & Editors. The actual developer of this free software for Mac is Digital Film Tools.
From the developer:
Power Mask is the first realtime, interactive tool capable of extracting almost any object in an image--even if you are dealing with fine hair detail, smoke, or reflections. As you simply paint along the edge of the object to be extracted, either the mask or the final composite can be revealed instantly. This extraction process creates what is known as a mask--essentially a black and white cutout.
You may want to check out more software for Mac, such as Smith Chart for Mac, Movie2Shot or TVPaint Animation, which might be related to PowerMask.