These days, the most economical (and legal) way to access the latest version of Photoshop is by paying an average of twelve euros per month on Creative Cloud. If Adobe's sandbox isn't an option and the budget doesn't allow it either, all roads lead to open source. GIMP has been the number one alternative for years, but there's also the editor Krita, which offers interesting resources for artists who draw freehand.
There are two things that beat me by a mile over everything else. The first is working with wood, and the second is drawing. I was so bad at drawing that I used to create circles using coins instead of a compass like the rest of the planet. It was torture during high school, and just seeing minimal details in image editors churns something inside me. Sooner or later I'll have to face that demon, especially in the CAD territory, since it's a critical resource to get the most out of a 3D printer. Meanwhile, I limit myself to studying the situation of different tools. Photoshop needs no introduction, but it's expensive for personal use, and its dependence on the cloud causes annoyance to many users. Of course, no one has forgotten GIMP. Nineteen years of development and a notable user base demand great respect.
Krita in Detail
Still, there are other options beyond the borders of GIMP and Photoshop. One of them is Krita, developed by none other than KDE. It has been with us for nine years, so we can't say it's a young application. In fact, we came across it in 2011, thanks to Nicolás's analysis. Krita offers all the basic tools we can expect from an image editor, but as its creators indicate, the software's priorities are sketching and painting. The number of brush presets is impressive, and although I've noticed a fewer number of effects, the riders of drawing tablets will surely know how to extract every last drop from Krita.
Availability and Stability
Krita is available for Linux, Windows, and OS X. As with other applications, the port of Krita compatible with Windows is one or two minor versions behind, but I must admit it has no stability issues, and this extends to 64-bit editing. Some of the drawings published on the official site of Krita are excellent, and there we can also find a healthy number of tutorials to start mastering it. Certain public institutions, such as the University of Paris VIII, have already replaced Photoshop with Krita. Do you think you can do the same? Don't forget to give it a look.
Official site and download:Krita.org