We Don't Gatekeep Art Resources | A Comprehensive List
Here's a list of some of the tools/sites I currently use or have used previously for works/studies. I'll separate it into Software/Utility, Reference, and 'Other' which will be just general things that could help you map out things for your experience with art.
**[Free highlighted in pink, paid highlighted in green. Blue is variable/both. Prices Listed in USD]**
Krita Painting app (PC) (my main digital art software on PC for 5+ yrs)
Clip Studio Paint [PC] [CSP 2.0+ allows for 3d modelling within the painting app and a lot of other cool features] [apparently allows up to 6 months free trial]
Procreate (12.99) [iPad/iPad Pro] (the GOAT)
Artstudio Pro [iPad/iPad Pro] (An alternative to Procreate if you enjoy the more traditional art app layout) -- I find this app handy when Procreate is lacking a feature I need, or vice versa. (you can easily transfer files between the two, but keep in mind Procreate's layer limit)
2D "Collaborative Painting/Drawing apps"
Gartic Phone (Pretty decent for 2d animation practice, but has a hard limit on frames)
Blender [3D Modelling, Sculpting + Layout] (PC)
Sculptris [PC] (it's an old unsupported version of Zbrush, but can help to get ideas out, and functions better than browser sculpting apps
Nomad Sculpt [iPad/iPad Pro] ($20) Works pretty well if you prefer a mobile setup, but it is a bit intense on the battery life and takes some getting used to
Magic Poser [ PC and Mobile ] Has both free and paid versions, I've made do with just the lite version before
Artpose ($9.99) [Iphone + Steam]
Head Model Studio [IPhone] A 3D head, with both a basic blockout version for angles, and a paid version with more detail
Cubebrush [simply search "[keyword] pose reference pack"], they usually have good results + they frequently have sales!
Line of Action [Good for Gesture practice + daily sketching], also has other resources built in.
Quickposes Similar to Line of action, more geared toward anatomy
Drawabox | Perspective Fundamentals Improvement modules (Suggested by @taffingspy )
Sketchfab, this skull in particular is useful, but there is other models that can help you study anatomy as well.
Pinterest can be good, you just have to be careful, usually you're better off just finding reference pack if you have the money, sometimes certain creators have freebies as well
Artstation Marketplace can be decent [make sure to turn on the Aye-Eye filter so it doesn't feed you trash], a colleague of mine recommended this head model for practicing facial blocking, there is also this free version without lighting.
Local Art Museums [Unironically good for studying old "master work" if you're into that, or even just getting some inspiration]
Brushes + Other Useful software:
I personally have used both of these brush packs before making my own
(I actually don't know how to share my daily brush set because I frequently switch between Krita, Procreate, and ASP, but once I figure that out I'll be sure to do that lol)
Marc Brunet's Starter brush pack [Technically free but supporting him for this if you like it is ideal, there's some good brushes]
Dave Greco Brush Pack [$3]
Gumroad in general is a good place to find brushes and art resources. *Note; for Krita specifically, brush packs are a bit weird, so it may require you to find different packs, or import them in a particular way
PureRef [PC] - Reference Compiler/Moodboarding
VizRef ($3.99) [iPad] - Moodboarding/Reference Compiler
Artist Youtubers/Creators that helped me improve/guide me along as a self-taught artist from when I first started digital art to where I am today:
Marc Brunet (YTartschool)
+ Observing a lot of speedpaint art by people whose work I enjoy on social media/youtube, trying to dissect their processes
If you've gotten this far, first of all, congrats, you can read a lot, and second of all, thank you for reading and I hope this helps! I'll continue to come back and update this if I find any new resources in the future, or if my processes change :)