I made a new video about the pencil, pastel and charcoal styles in the artistic stylize filter in G'MIC.
Last year I contributed some textures to the 2.7 version of G'MIC (free open source) which create nice texture effects. The intended use was for 3D renders, photographs etc. but I also found it useful in my Illustration workflow for creating a textured base for working into, creating textures for overlaying, or for converting a rough digital painting into a pencil style. Still need hand drawing skills of course, but it helps create nice textured looks.
Some pictures I've created using the filter in the workflow: