Collection of Cool Software

This is a collection of useful, cool, or otherwise nifty pieces of software that I have come across (or made). Most of them work on Windows (unless stated otherwise), and they're all free.

FFmpeg iotools
Number one solution for manipulation of multimedia files, with an overwhelming support for almost all conceivable audio, video, and subtitle formats. There are bitstream options, codec options, filters, options for multiplexing, demultiplexing, channels and a lot more. The command-line interface might not be intuitive at a first glance, but it has logic to it that one quickly gets used to, plus the web documentation is clear and easy to navigate. A collection of I/O software of mine, not much useful on its own but very powerful when combined with other software. pipeio allows one to connect to or create Windows pipes for use from within the console. passio is like Unix's cat. logio wraps each line of input with a formatted date and time prefix, useful for servers that were not born with such a feature. imgio reads a stream of images and stores them as temporary files, calling a command for each one of them. ffvars and ffcat are made specifically for FFmpeg, the former setting environment variables from FFmpeg video info, and the latter producing files in the format of FFmpeg's concat input format.
Ruffle CheerpJ
It's unfortunate that capable Flash emulators are coming with such a delay after its end of life, but at least there are some good ones. This works very well in the browser and handles various Flash movies reasonably well. It is still in development, and there are some issues that may arise with specific applications, but it is good overall. Like Ruffle for Flash, this makes it possible to run Java in the browser, including applets. There are not so many web-based Java applications compared to Flash, but there are still ones that you may want to run some day.
ForceBindIP ZeroTier
A launcher for applications that injects itself into the launched process and reroutes network communication that is fixed to a specific network to a network of your choice. This is especially useful when you run games (both old and new) that have a LAN multiplayer option but you want to use them when connected to friends over a VPN. This essentially decouples what applications like Evolve or GameRanger do. As far as VPN-enabling software goes, this is the best of all the solutions I have tried over the years. It is capable of connecting any two computers, be them behind a NAT or a particularly restrictive router, so that they are capable of direct communication. This is very useful for work, sending files, or playing games. The user interface is a bit lacking, but it is easy to get it working, eventually, and the overall capability of the software makes for it.
winevdm/otvdm NTVDMx64
Continuing with emulators, this one is for running Windows applications on Windows, specifically 16-bit Windows applications from the old pre-NT era. It comes with a 16-bit CPU emulator and implementations of old Win16 functions using the modern API. On top of that, it seems to be able to run some DOS software as well. Last of the emulators, this one is a modern port of the old NTVDM software for running DOS applications. Don't expect it to run all the cool games that you have (use DOSBox for that), but the text-based DOS applications should work very well. Its recent releases also support some 16-bit programs, but you may want to stick with winevdm, as it's easier to install.
IPXWrapper DxWrapper
IPX was an internet protocol used before the TCP/IP family became popular, utilized in many old games. If you want to play a non-DOS game that requires it (DOSBox already has an emulated IPX support), you can use this wrapper that uses UDP for communication instead. It also has a configuration allowing to choose a network, in case of a VPN. For games that use DirectPlay, the emulator can be added to the list of supported network services, and may well be the only thing that works. Another program useful for running old games is DxWnd's counterpart for running older DirectDraw/DirectX games. It contains a lot of useful fixes and configuration options and is, in my opinion, more usable than DxWnd as it doesn't require a launcher and could be easily bundled with an application.
3D-Analyze cnc-ddraw
This program started as a tool for improving performance of games on older GPUs, which you may not find that much useful, depending on your computer. However, it is also very powerful when running games that are older or lack sufficient graphics options, as it can tweak them to your liking. Notably, you may be able to use this to launch a game in a windowed mode which it didn't support natively. Another software for improving older games; this one serves as a ddraw.dll (DirectDraw) replacement. It can improve compatibility and performance, offers many more graphics options, and also contains a variety of shaders.
You've heard it correctly, the original Windows file manager is back! If you have always preferred it for some reason over Explorer, be it for its compact and yet functional design or its efficiency, now you have the chance to start using it again. There are also two versions of the application, one that has no functional additions from the old program, and one with improvements and tweaks to make it even better. Something for DOS this time, HBREAK is useful when running games or other programs that don't offer the luxury of being able to terminate them when the user wishes. This might have been more useful 30 years ago, but it could still help someone in DOSBox these days.
If the shell extension to open archives is not enough for you, you can use this utility to register an archive as a virtual drive, meaning applications that require to access the filesystem can be pointed to the archive seamlessly. Be warned however that some archives might not be directly browsable and would be transparently extracted before browsing this way!