Krita (usually pronounced /ˈkriːtə/ KREE-tə) is a free and open-source raster graphics editor designed primarily for digital painting and 2D animation. It runs on Windows, macOS, Linux, Android and Chrome OS. It features an OpenGL-accelerated canvas, colour management support, an advanced brush engine, non-destructive layers and masks, group-based layer management, vector artwork support and switchable customisation profiles. It is written in C++ using Qt.
I used this tool a couple times and it is really cool. I didn’t test everything, since it takes a bit of time to get to know every feature of it, because there are many of them. It is also trade-free, as there are no ads, trackers or the like. Also, you don’t have to trade your currency in order to use Krita. Therefore trade-free. However, I have to deduct a block, since the website is not that clean: https://www.directory.trade-free.org/wp-content/uploads/2020/11/6a527a1787e310a0284f7fb76c6ceca4.jpg – I give 4 of 5 blocks.