Character Design Visual Library - A collection of concept art for different character design types you can use as references. Also contains poses and links to tons of other resources.
Paletton - If you have trouble with color theory, you can use Paletton to give you a good idea of what colors go well together.
QuickPoses - Timed gesture drawing you can take (mostly) at your own pace. If you sign up, you can track your progress and even print out little certificates once you meet certain time requirements. Completely free, but they have an offline version that you can add your own photos to if you throw them 15 bucks.
Adorkastock - A DeviantART user who has tons and tons of photo references for poses.
PhotoPea - A free, in-browser copy of Adobe Photoshop. Doesn't have every feature, but still has quite a lot.
Font Matcherator - See a font you want to use in your own work, but can't find it? Take a screenshot, upload it to the Font Matcherator and it will try to find it, or ones similar to it. The font you're looking for might be free! The website itself, Font Squirrel, also has tons of free fonts hosted there.
@artist-refs - A defunct tumblr blog who used to reblog and tag every tutorial they came across. Has been on indefinite hiatus for years now.
/r/SketchDaily - A subreddit that offers 2 drawing prompts everyday. Good for when you can't think of anything to draw.
Blender - Probably well-known, but I still often see people ask for 3D software so: Blender is a completely free 3D sculpting program with literally every feature you can ask for. It's open source, meaning people can make plugins to add even more stuff to it. Extremely high learning curve, but it's very quickly becoming an industry standard because of how accessible it is.
Blender Froggy Tutorial - If you're just starting out in Blender, here's a good tutorial that will teach you the basics. May want to watch at 0.5x speed.
Joe Murray's Creating Animated Cartoons with Character - The creator of Rocko's Modern Life and Camp Lazlo put out a book about his cartoon/ character design philosophy a while back. It had a very limited printing run, and as a result, people started buying and upselling copies. To combat this, Joe Murray decided to put the whole thing online for free.
DrawABox - A website that teaches you the absolute basics of drawing. Goes very, very in depth.
KidPix - It's KidPix! In your browser! For free!
JsPaint - Original Microsoft Paint! In your browser! For free!