Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
Visily - The easiest and most powerful wireframe software for agile teams.
GIMP - GIMP is a multiplatform photo manipulation tool.
PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Learn SpriteKit by Design+Code - Make a platformer iPhone game from scratch in Swift 4.