Here is a collection of my favorite free software. (All below programs work on Windows, among other operating systems.)
Notepad++ is a program that everyone should have. It's an intuitive text editor, which handles large files with ease, supports tabs and context highlighting for all standard file types and programming languages. It has powerful user functionality including regex search and replace along with plugins of all kinds. I use Notepad++ on a daily basis.
Notepad++The best all-around video/media player (including DVDs). Should be considered one of your computer essentials. It's open source, no ads and no cost. It also has a built-in converter between media file types and useful command line callable functionality if needed.
VLC Media PlayerPaint.net is a good free photo editing software. Paint.net supports layering and 3D effects. It exports to all major photo extensions. It's very useful for everyday photo editing needs.
Paint.netThis audio editor is one of the best out there. It includes a variety of useful features such as audio filters, as well as noise removal.
AudacityKdenlive is a full feature video editor, a bit of a learning curve to use but supports all basic video editing needs. It's free, open source, and also runs on linux.
KdenliveDaVinci Resolve is one of the most powerful free video editors. One of its best features is 3D motion tracking. Note these complex features require a good amount of RAM and a nice graphics card. (The free version requires registration but can export in 1080p.) For a simpler and more intuitive video editor, see Kdenlive.
DaVinci ResolveAutoIt is a simple programming language that allows automating mouse, keyboard, and other user controlled behavior to perform computer tasks. This is especially useful for performing those repetitive computer tasks that we all face in life, like pressing an ok button 30 times every time a window pops up.
AutoItWamp server is a great local hosting enviroment for Windows. This allows websites to be tested locally before running them live. It can also be used for experimenting/learning backend development using languages such as PHP, mySQL, Python, and more. Installing this software is complicated. Be sure to follow all the instructions.
Wamp ServerBlender is an extremely powerful (but very hard to use) animation, video tracking, and 3D rendering software, among many other features that it has. There are many video tutorials online for using the software but it takes time to learn. When used to its full potential, the final image/animation looks real.
BlenderThe Institute for Advanced Physics' Mars Calendar allows Earth time to be converted to Martian time and vice-versa. It's a fun program to play with. Because it is an older Java application, there is a few extra steps to install it on newer computers. I have found installing from the ZIP file to be easiest.
IAP Mars CalendarWinSCP is a good FTP client with some advanced options including synchronized file viewing. This is useful when transferring/viewing files from a remote computer (such as a website server).
WinSCPScratch is a good program for learning the basics of programming and game design. But don't expect to make anything too crazy with it. There are no built-in export options; however, with some additional software, an exe file can be generated.
Scratch WebsitePuTTY is a client for connecting to a remote computer via command line. This is useful for connecting to Raspberry Pis and other networks.
PuTTYEvery Windows programmer should have this Linux shell. This is great for compiling C++ programs on Windows. With some registry editing, you can set this subshell to open in the right-click menu of any folder.
Installation InstructionsWant to write your own music but don't have a personal orchestra nearby? This free program let's you hear your soundtracks played by a virtual orchestra with a variety of customizable instruments.
MuseScorePython is the goto language these days for most kinds of automation on your computer because its easy and concise to write and has lots of library support. If you know what you're doing, just install and run python raw. Using annoying python distributions such as Anaconda have massive overhead and overcomplicate your life.
PythonThis is a super fast windows files and folders search tool. It will search your entire computer effectively instantly. Say goodbye to the ridiculously slow and even innaccurate Windows Explorer search bar.
Everything SearchA photo screensaver software for the modern day, featuring multi-monitor support (unlike the antiquated Windows built-in one). This is a great way to display the thousands of digital photos we've taken over the years but never looked back on.
gPhotoShowThese cool phone apps work on android, among other OSes.
As an alternative to Google Play, all of the apps in this app store are meant to be open-source (meaning you can read their code) with no ads or other privacy risks. You can find the basics, such as compass and flashlight apps, all the way to advanced apps you didn't even know existed. (However, don't be careless; malicious apps can sneak in anywhere so always do your due diligence before installing.)
F-DroidSignal is a messaging software similar to WhatsApp, except it's completely focused on privacy. Theoretically, no one else (except maybe the NSA) can read your messages, know who your contacts are, or see anything personally identifiably about you (which is not the case for any of the other major messaging apps).
SignalHoopla is a free service provided by many local libraries that allows you to borrow audiobooks and ebooks via your phone. Great for long drives or when you can't make it to the library to get a physical book. Check with your library to see if they provide this.
HooplaSimilar to Hoopla, this is another possible free service provided by your local library providing audiobooks and ebooks via your phone. CloudLibrary can have a different collection of items than hoopla so they're both worth getting if your library provides them. There are other apps like these as well that different libraries support so check with your library to see what's available.
Cloud LibraryComing soon: my favorite hardware devices
Best Q&A site, especially for engineering and software related issues.
stackoverflow.comW3Schools is a good resource for learning a new programming language. Plus, it's also a convenient quick reference guide. However, move to more in depth resources once you understand the basics of a language.
w3schools.comIAP is a great reference for physics resources as well as a variety of articles in their online magazine.
iapweb.orgRobowarner makes cool robots. Then, he explains how they work and has some videos of them doing amazing things.
robowarner.comSee what websites looked like in the past. Or if a page you're looking for is no longer online, see if it's been archived by the wayback machine.
web.archive.org