There are plently of art programs out there, but many cost money to buy. This article aims to help you find a free or open source altneratives to paid art programs.
The following programs are alternatives to digital painting programs like Paint Tool SAI and Corel Paintshop Pro.
Krita is a great program that is actively developed and has a plethora of features. The brush engine in particular is really nice. Similar to GIMP & Photoshop, Krita does more than just digital painting. You can do things like photomanipulation, and it offers a variety of file formats and templates to experiment with. Because there are so many features, the learning curve is going to be higher than with something like SAI, but since it's well laid out and gorgeous, you should be able to paint gorgeous stuff in no time.
Keep in mind, Krita uses a lot of RAM & CPU, and you might need a graphics card to keep the program running in a fast manner.
MyPaint is one of my personal favorites for a variety of reasons. 1) MyPaint presents itself in a clean, uncluttered workspace while allowing you to customize panels the way you like them. With a click of the tab key, all menus can be hidden, which is really nice. 2) I love the variety of settings in MyPaint's brush engine. If you hunt around, you can find a lot of really cool brushes that behave pretty uniquely. 3) Infinite, raster canvas. This feature is really great. You don't need to worry about creating a bigger canvas because it goes on forever and gives you unparalleled freedom. Although primarily developed for Linux, Windows builds are currently in the process of being updated. (Mac builds are there too!) MyPaint is lightweight and runs fast, even on low powered machines like my Atom based tablet.
Fire Alpaca is similar to Paint Tool SAI but offers a slightly different feature set. Since it's available for both Mac & Windows, it's a nice SAI alternative to more people. There's not a lot of brush customization in Fire Alpaca, but you do get line smoothing and a water brush tool that's really nice. I am also a fan of the way you can quickly set up perspective grids. Fire Alpaca is nice and is actively developed, meaning new features are implemented all the time.
Alchemy is less of a program for painting and more of a program for sketching and design creation. There's a lot of neat things you can do with symmetry and randomness, which is great if you need to paint randomly in order to generate ideas.
Autodesk Sketchbook is free in the Copic edition and in the Starter/Essentials edition. You get less features, but there's no free trial counters which is really nice. Sketchbook Copic stimulates the look of markers while Starter/ Essentials gives you a few, nicely designed tools to paint with.
Photo EditorsThese programs are for photo editing primarily, but some are used for digital painting is well.
GIMP is a lot of things. It's almost like Photoshop in complexity, although some tasks require a few more clicks than they would in Photoshop. GIMP has come a long way since its earlier builds and can do a lot of different things. Since GIMP is so popular, you can find plenty of nice tutorials and plugins.
Paint.NET is an image editor that is way lighter and faster than Photoshop, but still offers a good amount of features and flexibility.
Lots of available plugins and is still actively developed. Keep in mind, it's only available for Windows, and not the RT version.
RawTherapee is a digital darkroom developer/image processor like Lightroom, which means it's great for processing the RAW file format. It also supports Adobe Lens profiles, so you can do lens based adjustments.
darktable is similar to RawTherapee, but offers masks. RAW processors are nice because they are nondestructive. The two programs are similar but try both and see what your personal preference is.
Picasa is a great piece of software designed to organize your photos and edit them as well. It offers ways to easily share your photos on Google+ and other social networks. In addition, Google is constantly adding new features and photo effects. Photo editing is also nondestructive.
Illustration & Graphic DesignInkscape is a great vector and illustration program. It's got many plugins, features, and all kinds of resources/ tutorials written for it. You can do a lot with Inkscape and it's available for all platforms.
Draw Plus by Serif, the creator of Afinity Designer, offers a lightweight graphic design program for Windows. I haven't tested it, but it seems pretty competent.
3D Modelling & AnimationBlender offers an amazing set of features: animation, rendering, compositioning, rigging, sculpting; I highly recommend you hop over and take a look at the extensive feature set! This comes, however, with a steep learning curve. However, if you have a project that demands complexity and options, Blender might be the program for you. It also is available as a portable app, which is super great.
Daz3D is not normally free, but if you register, it is! You can do many things, but its main highlights include animation, CG, 3D design, and storyboarding.
Sculptris allows you to sculpt 3D models, and is made by the creators of ZBrush. In addition to sculpting, you can paint your 3D models and light them in very realistic ways.
Hopefully this article has helped you in some way!
Have you ever used free or open source software in your work? If not, are you planning to now? If you've ran into any others, feel free to share links to them!
Feel free to answer in the comments below!