Resources?
Things that I use, used, or just simply like. Mind you, I haven't participated in the creation or maintenance of any of these, I just think they're neat and should be passed forwards.
Links in each title
Software: Writing
LibreOffice
A free "office suite", essentially an open-source alternative to Microsoft Office, and what I have been using to write for some many years now. Has everything you may need to start your novel, and much more really, though to be honest I only use the Writer (Word) and Calc (Excel) programs.
As I've said somewhere before, I can't comment on how it compares to the paid stuff, but it has all the basics for writing and formatting documents, and hasn't disappointed so far, outside the still somewhat lackluster spellchecker.
Recommended to try if you want to start writing anything, but have no idea what software to use.
Software: Arts
Blender
Out of everything here the software that needs the least introduction. THE go to 3d software for those of us who can't (or won't) use the Autodesk stuff, free and open-source.
It's great, and only got better with time. Has strange ambitions to be an omnireaching program, but considering the breadth of things I use it for, who am I to complain? Mariwa: An Ivian Tale's cover, for example, was pretty much entirely created and composed in blender, outside of some minor filtering and the title.
Want to do 3D modeling? Sculpting? Texturing? Drawing? Animation? Image compositing? Video editing?! Porn?! Blender got you covered, always!
Recommended for anyone who has any interest at all in 3D art. Specially recommended for anyone who checked out the earlier versions (say, 2.x and around) and bounced clear off, I've been there and things have gotten much better, believe me!
Krita
Free and open-source 2D art software.
It's no photoshop, unfortunately, and again, I can't say how well it compares to the other paid stuff, but I like it, and from what I've gathered other people with more, broader experience with drawing programs also enjoy it fine.
See the background images on this site? All made with Krita! I've also used it previously to work details on textures and, as mentioned before, to add the finishing touches on covers and renders. It's pretty good, and comes with a decent amount of brushes, though it does have a certain learning curve to it.
Recommended to at least check it out if you have an interest in 2D art and either no money to spend on software, or no will to pay for them. And hey, at least it's better than [REDACTED]!
Effekseer
An odd duck of a free and open-source arts software, focused on the creation of special effects and particles for game engines.
Actually pretty complicated compared to the other software I recommended, but once you get it going you can make some pretty amazing stuff with little to no resources. Don't really have any examples to give at hand right now, but check their sample effects section.
Recommended for anyone interested and who has the free time to learn the ropes. Take it for a spin, it's actually pretty fun.
Others
The Models Resource
Hosted by The VG Resource, similar to the Spriters Resource but focused on 3D models instead. A great place to study the work of professionals up and close.
Polyhaven
Hosts countless 3D assets, from textures to models to HDRIs, all free and granted under a CC0 license. Hyper realism isn't really my style nor goal, but if you have any interest in 3D art this is a place you must absolutely keep in mind, their work is insane.