After some testing, I've pushed the GIMP snap to the stable store channel. GIMP (The GNU Image Manipulation Program) is an image editing and manipulation tool similar to Krita, Pinta, Paint.NET, and Photoshop.
sudo snap install gimp
The yaml is in my repo if you're interested in learning how it was built, or contributing to it. (It will be moved to the snapcrafters repo eventually.)