Pros: FireAlpaca is an easy-to-learn software oriented towards illustrators and cartoonists. I would recommend this program as a first step for those wanting to learn digital illustration. It is available in 10 languages. FireAlpaca also has animation and GIF capabilities.
Cons: I haven't used this program enough to know its flaws. Feedback is appreciated.
Official Tutorials: https://firealpaca.com/en/topics/
Pros: Gimp is a software with a variety of capabilities and uses; It can essentially do anything that Photoshop can do. Painting, illustration, photo editing, and even animation and GIF creation can all be done with Gimp's expansive set of tools. Gimp has been around for decades, so there are many user-created resources online to help you learn.
Cons: User interface is complex, takes a while to learn for inexperienced users.
Official Tutorials: https://www.gimp.org/tutorials/
Donate: https://www.gimp.org/donating/
Contribute: https://www.gimp.org/develop/
Pros: Krita is a feature-rich software oriented towards painters and illustrators.
Cons: I haven't used this program enough to know its flaws. Feedback is appreciated.
Official Tutorials: https://docs.krita.org/en/
Donate: https://krita.org/en/support-us/donations/
Pros: Another great, lightweight freeware with lots of features.
Cons: I haven't used this program enough to know its flaws. Feedback is appreciated.
Donate: https://www.getpaint.net/donate.html
Pros: Photopea is a web-based image editor, meaning you don't have to download any software to use it. Great for quick and simple image edits.
Cons: I haven't used this program enough to know its flaws. Feedback is appreciated.
Official Tutorials: https://www.photopea.com/learn/
Donate: https://www.getpaint.net/donate.html
Pros: Procreate is an iPad Pro only program which is designed for painting. It is lightweight and has a simple user interface. I recommend this program for beginners wanting to get into digital painting.
Cons: *Procreate costs $10, but I'm including it in my list because it is a one time fee, and comparatively very cheap for such a powerful program. This software is not designed for precise image editing (The fill tool is subpar, in my experience). Procreate is unfortunately only available on iPad Pro.
Official Tutorials: https://procreate.art/handbook/5.1
Contribute: https://folio.procreate.art/discussions/3