Atlas is Windows-only for now -- but the full source code is included, which means that anyone can compile a Mac version. Here's more from Stefan...
"So what’s tone mapping you ask? According to Wikipedia:
The technique is particularly useful if you have high dynamic range images, such as rendered CG-imagery in floating point color-depth (OpenEXR) or HDR photographs, and you want to bring their broad spectrum into a range more suitable for display on a computer monitor or television screen."
Tone mapping is a technique used in image processing and computer graphics to map a set of colours to another; often to approximate the appearance of high dynamic range images in media with a more limited dynamic range.
Note: Stefan released [umm sorry, teased instead] another filter recently, Edgar, "which is designed to work in combination with Normality and generates squeaky clean cartoon outlines. Edgar uses a novel, proprietary algorithm developed specifically for the purpose of converting normal passes into line art for use in cartoon and anime productions."