Digital Projects Toolkit

Web; iOS/Android - free.
Using BeFunky, you can edit photos, apply effects, and create collages.

Web - free.
Canva Photo Editor lets you make quick edits to images - filter, adjust color, crop, resize, rotate, and flip.

Web; Windows/Mac; iOS/Android - free.
Polarr offers advanced photo editing tools in an easy-to-use format.

Windows/Mac - paid.
Adobe Photoshop lets you create and enhance photos and images: it offers advanced tools for editing images in a variety of ways.

Windows/Mac/Linux - free.
GIMP (GNU Image Manipulation Program) is a free and open source alternative to Adobe Photoshop: it offers many of the same image editing and retouching capabilities.