https://www.gimp.org/ - GNU Image Manipulation Program or "GIMP" is an open source cross-platform that is my favorite for doing 2D graphics, especially manipulating images and post-processing.
builder.blender.org - Development Versions of Blender 3D - These versions have the latest features, but may be unstable. You can help test them and report any bugs.
NOTE: You should be careful about using development versions in production projects.