This is a collection of resources and software that I have found useful for 3D artists in one way or another. Some are free and some are paid resources.
Textures.one - The best place to start at the moment, it is like a texture search engine, searching through a set of the texture sites below as well as some smaller collections.
Texturehaven.com - This site has excellent texture quality made from 3D scans. All cc0 and a historical theme.
cc0Textures.com - This site is a goldmine for anyone needing textures for most kind of scenes and architecture visualization.
cgbookcase.com - Same as above, a growing texture library of high-quality cc0 textures.
sharetextures.com - Slightly newer site than the above ones but you can find some good textures here. Some textures require you to join the patreon page for access.
3Dtextures.me - To me, this is a newer site but has one of the highest quality overall.
Chocofur - Got high-quality textures only requirement is to create an account to download them. They also have a nice 3D model collection under the cc0 license.
VirtualShade - Varying license between cc0 and cc-by. Even if the collection is quite small, whats there has excellent quality.
Texture.ninja - A large collection of image textures. only photos, no texture maps. But the size of the library makes it worth to check out.
Duion.com - This is a library of cc0 textures. Mostly photos that are taken to be used as textures, not properly prepared to be seamless or anything though so they need some work.
3D-wolf.com - just a handful of textures on the page, but at the bottom, they have a link to a larger library of textures on a Google Drive repository.
HDRIHaven.com - Possibly the site that has sparked life into multiple of the texture sites above. The goto place for hdri images.
Pixabay.com - only cc0 images, larges library, and fast-growing, no longer cc0 to prevent their images to move to other libraries. But other than that they are free to use.
Stocksnap.io - cc0 images, smaller library, may find more unique images here
usplash.com - continue on with the good stuff
Pexels.com - like the two above I guess
iconmonstr.com - it’s not cc0, can’t be used in logos, etc. but a very permitting license.
Blendernation - The go-to place for Blender related news
Blender Today - Blender news and community
Godot engine - The open-source game engine
Armory 3D - Game engine running on top of Blender
Unity - Popular game engine
Unreal Engine - Slightly more advanced game engine
Lumberyard - New game engine based on CryEngine
Krita - the number one open-source painting app
Gravit.io - interesting vector graphics software
Inkscape - The go-to open-source vector art program
Mischief - Cool infinite canvas painting application
Rawtherapee.com - Open source raw image file processing
Blender - Needs no more introduction
Makehuman - Software for creating anatomically correct human models
ProRender - Alternative render engine that runs in Blender
Sketchfab.com - Show your 3D creations on the web
vb-audio - Advanced audio mixer tools
Open Broadcast Software - record and broadcast
Audacity - Improve your audio
Kuadro - Reference image manager
Digicamcontrol - control your DSLR from your computer