KolourPaint
http://www.kolourpaint.org/
KolourPaint is a free, easy-to-use paint program for KDE (a desktop environment for UNIX).
It aims to be conceptually simple to understand; providing a level of functionality targeted towards the average user. KolourPaint is designed for daily tasks like:
- Painting - drawing diagrams and “finger painting”
- Image Manipulation - editing screenshots and photos; applying effects
- Icon Editing - drawing clipart and logos with transparency
It’s not an unusable and monolithic program where simple tasks like drawing lines become near impossible. Nor is it so simple that it lacks essential features like Undo/Redo.
The main difference between KolourPaint and most other “simple” UNIX paint programs is that KolourPaint actually works. KolourPaint is opensource software written in C++ using the Qt and KDE libraries. It is developed in the KDE repository and is shipped with KDE releases.
KDE / kolourpaint
https://github.com/KDE/kolourpaint
Documentation
Kolourpaint Handbook on docs.kde.org
https://docs.kde.org/stable5/en/kdegraphics/kolourpaint/index.html
If you have KolourPaint installed, an offline copy of the handbook is accessible from the “Help / KolourPaint Handbook” menu item.