GIMP (short for the GNU Image Manipulation Program) is a free software raster graphics editor. It is primarily employed as an image retouching and editing tool.[3] and is freely available in versions tailored for most popular operating systems, including but not limited to Microsoft Corporation's Windows platform, Apple's Mac OS X, and Linux.
Paint.Net
If you're used to Photoshop you'll get on with Paint.Net.
I don't use Photoshop now.