There's an entire category in the forum dedicated to showcasing projects, which is always amazing to look through. (Link here) but there's a lot of projects that are still in progress, so this kind of thread where people announce what they're working on currently, even if it is incomplete, is nice.
I'm working on Onbox, which is a backend social networking server that implements Mastodon's API. It's still very much in progress and there's a lot of work left to do, i haven't worked on it for a while because I've been busy with other stuff, but i'll get back to it soon.
As for cybersecurity libraries in nim, you could search for packages related to cybersecurity in nimble.directory or look through the awesome-nim GitHub repository. If you describe what you're after in more detail in this thread then someone else might be able to help find what you're looking for.
Nim lacks some mature audio libraries, so I had to return to C++.
That is probably true but you might be interested in this:
https://codeberg.org/SpotlightKid/nim-audio-dev
Also, using C libraries from Nim is super easy and many C++ libs have C interfaces.
portaudio, fftw3, DspFilters, libusb, others.
Have a look here, https://nimble.directory/ several of what you mention have bindings, don't know the state of things.
DspFilter seems more something to translate to Nim, simmilar for parts of librosa