GMIC is a free and open source photo editor. With it, you can apply tons of adjustments, filters, and effects to an image, some of which are not even available on Adobe Photoshop. GMIC can be run in two different ways: by integrating it as a plugin on GIMP, or in standalone format, in which case no additional program is required to run it. When you open the program, simply choose the image you want to work on. To find it, you must first determine its format, since by default, it only allows you to open .png, and you have to select .jpg. After opening the image, you'll find a whole series of effects and filters that you can apply to it. You can apply artistic effects, deformations, gradients, additional light, additional shadows, mirror effects, 3D effects, colors, and much more. Most of the effects on GMIC are adjustable, so you can move the sliders to modify aspects of each one, such as its transparency or intensity. When you find the effect or filter you want, click on apply at the bottom of the screen. After applying it, you can export the image in the format of your choice. One of the best features of GMIC is the ability to double the number of pixels in an image thanks to an open source algorithm. In short, if you're looking for a comprehensive editing program, don't hesitate to download GMIC.
