Pixabay - hard not to know this website, but in any case, you don't know it's listed here. You can search there for free images, vectors, and videos. Their database is huge: over one million items. You can join Pixabay team as a member, upload your own content, and receive donations from sponsors. Read carefully licensing for each image you are downloading.
Pexels - a resource of pictures, video clips, not such big like Pixabay though. You can credit authors, donate them or join Pexels' team with your own content.
Unsplash - a source of free pictures taken by various authors. Read carefully license for each photo you are downloading. They will be very pleased if you join them with your camera.
FreeImages - free for personal and commercial use, but not standalone usage allowed, so you can't use it to create texture or 3D package for resale.
Reshot - all photos published on Reshot are free to use, both for commercial and noncommercial purposes. It means Royalty-Free images, no public domain, unfortunately.
CC Search - Search engine with options available: use for commercial purposes and modify, adapt. It delivers aggregated results among others from Flickr, Behance, Wikimedia and some museums.
Free Textures sites
CC0 Textures - an aggregated search engine which helps you to find free textures among many different websites, the first place you should look for CC0 license textures.
Share Textures - free PBR textures database with some ads display. To get some extra textures you need to become their patron.
Texturify - free textures for CG artists, not tiled, but you can create your own wit help of Texturify.com, actrually I created this site a few years ago, but photos are not mine.
Textures / formerly CG Textures - it is paid service but lower resolution textures can be downloaded for free. You will find almost everything here, probably the most complex resource out there. Register to get access to lower resolution textures for free.
Texture Ninja - public domain textures, most of the are not tiled. Use it if you want to create your own textures and don't have time or possibility to shot your own.
Texture Heaven - Scanned textures for free by Rob Tuytel, the good thing is that all textures are CC0 (public domain), so you can use them even to create your own paid content.
Free 3D modeling and sculpting software
Blender - completely free, fast and versatile 3D package, you can model, render, animate, do compositing and even 2D animations. It has a very large community of friendly users and its new 2.8 interface makes it easy to learn. Switched from Modo to Blender recently and feel more creative now. Go with Blender and you won't need anything more!
Sculptris - simplified version of ZBrush but completely free, very user-friendly. Although stripped down it has a lot of potentials especially if you are just starting with 3D sculpting.
Meshmixer - Autodesk free mesh repair and sculpting software. It allows you to remeshing, mesh simplification, hole filling, bridging, mesh smoothing, do cuts, automatic alignment of surfaces and much more. Very handy tool!
nanoCad - Actually it is Freemium. If you are into CAD and don't have money to pay Autocad license, you should definitely try this one, and if you like it you can purchase its more featured version.
SculptGL - SculptGL is a digital sculpting web app, with sources available on GitHub, so you can run it on your own web server. It is so cool that Sketchfab created their own fork of this web app, you can test it here.
Paint 3D - Very simply 3D and 2D painting app from Microsoft, available for Windows 10. Give it to your children to play with or use it for spontaneous prototyping. Donation driven service.
Free texture creation software
Materialize – Free texture creation software. It has no installer, just download it and unzip. To begin load diffuse map (letter O in Diffuse Map panel), and go step by step creating Heigh, Normal, Metallic, AO Map and so on. You can make tilling texture with Materialize, but it has only two algorithms for tilling only and no patch tool. This is the most popular app for free PBR texture generating, luckily if you are Windows user. For many users, this app is everything they need, but I would consider spending some cash on better commercial software.
PixaFlux - only one free Substance Designer alternative I could find. Not tested yet.
AwesomeBump - Windows and Linux (Ubuntu) tool for creation PBR textures from images. It has no installer for Windows. Download, unzip it and run executable. I like its UI more than Materialize. It has more control over the process of creating maps. You can even load your own .obj model for 3D preview. The last update on GitHub is from 2016. I am wondering why such a great tool is not developed anymore.
Armor Paint - Actually it is available to download for 16€, but you can compile it yourself from source code available on GitHub and use for free.
Blender - yes again Blender. It has node-based compositing capabilities, so you can process images from Blender or rendered externally. it is also very good for fast and complex compositing. If you are rendering in Blender why you should look somewhere further? I only don't, especially like its lens blur filter.
HitFilm Express - Full 2D and 3D compositing software, freemium. You can buy additional functionalities in Add-on Store. In contrary to After Effects it has a much faster preview because is multi-core and GPU accelerated.
Natron - Open Source Compositing Software, extensively developed thus sometimes not very stable, but I really like it. Its UI reminds me Nuke, and is OFX compatible. It has a tracker, keying tool, multi-layered rotoscoping. It is also very fast thanks to GPU acceleration.
Fusion - GPU accelerated freemium (see comparison), node-based compositing software by Black Magic Design. You can find it inside a free version of Resolve. It features camera tracker, rotoscoping, stabilization, keying, and everything you'd need. If you are looking for quality lens blur it is also here.
Free digital painting software
Krita - 100% free and Open Source digital painting software. Krita has 9 unique engines to customize your brush, you can paint with particles, shapes and even filters, stabilize your brush, create patterns and even simple frame-by-frame animations. This software has so much to offer that can be a little overwhelming, so take your time and watch tutorials and read manuals, it is very powerful! A very good alternative to Corel Painter.
Artweaver Free - freemium painting software. Free only for private and non-commercial projects. A very simple interface and realistic brushes. Windows only.
Mischief - freemium digital painting app. The free version has no layers, custom backgrounds, and few other things, but for 25$ you can get the full version which is cheap as a beer for what it does!
MediBang Paint Pro - if you are into manga or comic drawing you should definitely check this out. It offers comic panel creation, page management, it has pre-made tones and backgrounds to start quickly comic drawing. It's for Windows, MacOS and iPad , so you can make your comic drawings everywhere!
FireAlpaca - available for Windows and Mac, lightweight app, which can run smoothly even on the old computer. Very easy to use and children friendly, offers unique brushes, comic templates, 3D perspectives and much more.
Free video editing software
DaVinci Resolve - non-linear video editing (NLE) application for Mac, Windows, and Linux. An industry-standard software for coloring videos. A free version is not so stripped down, most users won't need extra features from the paid version. Node-based workflow gives you a lot of flexibility and built-in Fusion compositing software makes it a real workhorse for a serious filmmaker. This is a professional and really advanced app.
OpenShot Video Editor - a free open-source video editor for Mac, Windows, and Linux. It offers a plethora of video transitions. To generate animated video titles you need to configure it to work with Blender. Good for beginners, very well designed user interface, although it looks a little bit outdated. Use it if you have no time to learn more advanced video editing software.
ShotCut - Cross-platform, open-source, codecs independent video editing app. It features support for 4K resolutions, audio filters, track blending modes, chroma-key, and much more. I need to give it more time because it has very interesting features. Definitely worth to give a try.
iMovie - only for Mac and IOS users. It is very simple and easy to use. I use it on my iPad while traveling, and to quickly deliver short clips to my friends or family.
HitFilm Express - it is not only a compositing program, but you can also edit the video easily with it. Freemium, but still very useful, if you miss some functionalities you can purchase them in separate add-on bundles.
HandBrake - GPL video converter. I used instead of old and outdated Adobe Media Converter that comes with AE CS6. Download and install just this one. You won't need any other video converter.
Free audio processing software
Audacity - free, open-source audio recording and editing software. It's very light and fast, multiplatform (you can compile it even on FreeBSD). It supports VST plugins but only 32 bit. I use it for voice recording and quick edits, normalizing and noise reduction. For simple tasks it's perfect. You can install additional plugins from here.
Cakewalk by BandLab - complete Digital Audio Workstation for music creators now it's free! Cakewalk (brand) was acquired in 2013 by Gibson and in 2017 Gibson announced it was ceasing Cakewalk development. In 2018, BandLab Technologies purchased some of Cakewalk, Inc.’s assets, and continued SONAR development as part of its portfolio of freeware DAW software. You need a Windows PC to run Cakewalk and install BandLab manager to download Cakewalk.
Traction 7 - free DAW for all music creators. Fully functional version, no track or plugin limits. Perfect app to start recording your music. Easy to learn interface, VST support. It runs on Mac, Linux Ubuntu, and Windows.
Studio One 3 Prime - Studio One Prime is the free version of Studio One. Although it has no VST support and its functionality is limited, it's still a very creative tool not only for music creation beginners. I highly recommend Studio One as a Cubase alternative. I think it's much better in terms of productivity and doesn't require Steinberg's USB dongle.
Reaper - fully equipped DAW, actually not free, but the trial version is 60 days and never expires. Discounted license is 60$ only, which is a really not much for such advanced price of the software. I don't use it personally, but it is very popular DAW among many musicians. Try it, maybe it suits your needs.