GIMP, the GNU Image Manipulation Program, or better known as the free and open-source graphic/image software to Adobe Photoshop. (in layman's words: a poor man's Photoshop).
GIMP runs on multiple platforms. However, until now, in Mac platform, it only runs under X11 Windows environment, which is inconvenient and not smooth (compared to other native Mac apps).
From v2.8.2, GIMP is available as native Mac app.
Get GIMP at gimp.org.
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