Adobe Photoshop Alternatives

Many of the following programs can be used as an alternative to Adobe Photoshop (a popular raster graphics editor).

FireAlpaca, Windows and Mac OS X, free

PaintTool SAI, Windows, $50

Paint.NET, Windows, free

GIMP, free, Windows, Mac OS X, and Linux
This program is very powerful, but can be difficult to use.

Pixelmator, Mac OS X 10.9+ (App Store), $29.99

Pixlr Editor, web-based
This also has iOS and Android versions.

Affinity Photo, Windows and Mac OS X (10.7+), $50

Acorn, Mac OS X 10.10+ (App Store), $30

PaintShop Pro, Windows, $80

Seashore, Mac OS X, free

Artweaver Plus, Windows, $40 (a limited free version is also available)

Krita, Windows and Linux, free

Pinta, Windows, Mac OS X, and Linux, free

Xara Photo & Graphic Designer, Windows, $90

Photo-Brush, Windows, $55