What are some alternatives?
When comparing Krita and Adobe Photoshop, you can also consider the following products
GIMP - GIMP is a multiplatform photo manipulation tool.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Paint.NET - Paint.NET is a free image and photo editing software.
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.
Sketch - Professional digital design for Mac.