Definitely! Two of the three main tools used are commercial products (Genetica and Filter Forge, texture creation software) But one of the main goals of the Screaming Brain Studios project is to provide free alternatives and techniques with software that doesn't cost a dime so everyone can make their own! The third tool used is a free skybox utility called Spacescape that creates images for 3D skyboxes, but specifically works with noise generation and point clouds for creating stars and nebula clouds, whereas the two commercial tools use a large, node-based visual scripting process that can be much more complicated. To make them seamless, I use the Synthesis node in Genetica, but it is entirely possible to use the Make Seamless function that comes with GIMP to get similar results!
While they are not quite finished yet, I will eventually be releasing some tutorials on my website about creating nebulas and starfields in different utilities, or tools like GIMP! All of the SBS Graphics Packs have been made using the same tools and utilities, along with a few secret tools that are completely unavailable to the public, in order to maintain the same sort of visual style. But it is my goal that users be able to replicate or recreate as much of my techniques as possible in software that is currently available! Thank you for the feedback! :)