SQL - understanding how to interact with databases will be an incredibly useful skill for whatever rabbit hole you next want to fall down.

FOSS, learning curve, and niche field? I got you. VLSI layout software or SDR (software defined radio) software.

VLSI layout is kind of software allows you to design electronics hardware at the silicone/transistor level. IOW you have to draw the layers of materials that form transistors (cross poly silicon and p/n-diffused silicon to form) and connect them to metal layers. Learn how NAND and NOR gates are actually formed. Make a 1 bit data storage (flip flop), half adder, full adder. Go as far as you want.

Example software:

• Magic (what I used in school): https://opencircuitdesign.com/magic/
• klayout: https://www.klayout.de/

SDR. Less intense, but also niche and gives you lots of related things to learn/branch in to.

Can be used to receive and decode radio/satellite transmissions. Normally people would buy hardware and use software locally, but some people make their receivers accessible on the internet (websdr) which can give you a first intro to it. After you capture data you can run it through other software to decode (depending on what it is). For example, you can capture raw weather image data from satellites and decode it to get the images that the satellite is transmitting as it's capturing the data.

A list of some SDRs you can access over the internet (doesn't require hardware purchase to use): http://websdr.org/

It probably won't be immediately obvious how to use either SDR or VLSI software but you asked for niche and learning curve, so enjoy. ;)

EDIT: Fixed some typos and grammar.

ssh and scp (secure connection and file transfer)

grep (the standard command-line search tool)

sed (Stream EDitor, good for find-replaces once you learn how to use it)

awk (can operate on text files or command output that's organized in columns)

sc (terminal-based spreadsheet)

trash (safer replacement for rm that moves things to your desktop's trash directory instead of deleting immediately)

There's always software reverse engineering. As bad as it may sound to some people, the US NSA has a github repositroy for a tool known as Ghidra, under Apache 2.0 license, so you can look at the source code and determine whether or not it's spyware. If it's actually NSA quality, you know it should be good enough for reverse engineering old software that won't land you in trouble if found out by the original devs. Last update was 2 months ago.

I tried a little bit but have yet to go very far at all with it since I am an idiot who thinks he's smarter than he really is.

Though, taking a page from your book, I am interested in looking up rekordbox now.

One week of keybr.com to improve touch typing skills, which should serve you across all your IT endeavours... Unless you choose to learn gimp and drawing stuff :P

Factorio

Ardour, it's a FOSS Digital Audio Workstation

https://ardour.org/

https://buttplug.io/

Sketching 3D in FreeCAD.

You could get JOSM and become an OpenStreetMap editor. https://josm.openstreetmap.de/

Also install gentoo.

Mmkay thank you, this is such a great thing to ask.

Blender and buy a 3D printer afterwards

Lilypond. Its music software. Learning it will keep you occupied for at least a week.

Emacs

You can do really neat thinga in QGIS -- like make your own professional quality maps, make map animated gifs, etc

some suggestions for your consideration in order of empowerment and learning curve first,

• AWK
• ffmpeg (~ & imagemagick ?)
• bash, zsh, or fish
• kew (it's just a really simple nice tui music player, no fuss). (... "Am I the only fun one in Digit's list here?" -- kew)

n_n

Some other things that sprang to mind, (generally tending to more gui things, some distro/packagemenent things)... audacity/tenacity, fontforge, gimp, gentoo and portage, bedrocklinux and brl, peertube self hosting, forgefed self hosting, suckless.org's tools, CRUX or KISS/Carbs, just playing around in stellarium, playing around in pioneer space sim, learning how to evade humanity's detection as an ai in the game called singularity, ;3

Oh... Here's an idea for you... Learn a text editor.

Think it's not fun?

Depends on which text editor you pick, and how much the fun suits you. ... Emacs has so many things (including games, like tetris and doctor). Even neovim has some extra things (~ opencode runs on neovim... tho it's not the same, lol). Or maybe you want something simpler, like nano, mcedit, or fin (I wrote fin, don't use it, it's scruffy... and only able to do that from learning some of the things mentioned, and more).

Yay for learning. Yay for asking for what other fun things to learn. Good post. Good question. ... Sorry my answers were not better. Heh. Caught off guard, answered just what first sprang to mind. n_n Doubtless many other more fun things exist.

Blender

I don't have any suggestions, I just want you to know that you're delightful

There are a lot of newer node-based 2D editors (covering both vector and raster) like Graphite and PixiEditor. I haven't tried these... still wondering if any could easily do stuff like SDF textures or simpler mesh creation (2D workflow, part/face vertex color, maybe 3D via extrude/revolve).

There's also Wick Editor for a potential spiritual successor to Flash.

vi

FreeCAD

Learn Krita. David Revoy, artist of Pepper and Carrot, has a ton of great tutorials on using it.

How did you go about the excel learning? I find it to be too busy an area to get to parts I want to learn about, mostly pivots and formulas like you

I'd say GIMP for photo editing would be a good one to learn. It's come in handy in a pinch both at home and at work when I've needed something done up real quick.

I know you said software, but I would like to suggest a musical instrument. They still require learning a new language and typically provide a huge level of self satisfaction. A cheap keyboard or guitar can provide literally thousands of hours of study.

Stage lighting controls are extremely fun to learn. DMX, ArtNet, etc. QLC+ is free and open source, there are TON of other ones as well (like controlling big stage lights with a Wii controller so they move like you).

There are simulators, but the prettiest I've seen so far is https://github.com/AcChosen/VR-Stage-Lighting. Despite its name, you don't need vr for it but if you do, you can watch your lightshow as if it was real!

OpenSCAD. 3D modeling as code.

I've gotten a lot out of it, and their tutorial is excellent.

Ansible

Learn the basics of a couple of FOSS audio-software staples.

LMMS - tracker

Audacity - Audio recorder

Docker and Docker Compose. Once you know that, you'll be able to self host almost any FOSS.

Voicemeeter potato. Enjoy learning how all your audio devices work, and how to add noice effects.

Latex is worth knowing, its most commonly used for academic papers, but it opens up a whole world of scripting automated documents. But, to make it really interesting, throw in tikz and/or pgfplots for some interesting power tools. Tikz does A LOT, and is really powerful. But can definitely be overwhelming.

Godot. Start with an idle game, move onto more. Just don't make a horror game, way too many of those and a lot of them are bad.

Learn you a Haskell!

https://learnyouahaskell.github.io/

libreoffice if your using excel.

• MuseScore 4 is a (the!) free music notation software. It is genuinely fantastic. It's also a lot of fun, if you know some notation basics and want to play around.
• Darktable is a Raw photo editor in the vein of Lightroom. Except where lightroom is sleek, polished, user friendly and Adobe (🤮), Darktable is FOSS, and clearly so both in the design and functionality: it could easily make a UX designer cry, but if you're willing to give it a try, there does not exist a more potent raw editor on this earth. Lightroom is a toy in comparison. (Now whether you need that is another question... But I've been using it for more than 10 years, and am still finding new, incredibly useful sub-menus, drop-down contexts on hidden sliders,...)
• rmpc is a really cool TUI music player

Bash. If you use Linux.

OpenFOAM. If you ever want to figure out the aerodynamic qualities of a cow. This may take more than a weekend.

Meshtastic (Software and hardware).

My suggestion already submitted was Blender, but any of these ideas require a purpose. I don't think you truly learn an application or language (even human languages!) if you don't have something you're trying to do with it. Even music (it's a language), you can learn how to play something, how to put together notes and sounds, but you really start figuring out how to do things when you have a need to accomplish.

I would say 90% of my coding and application knowledge comes from decades of having a need or inspiration to do something, and having to find the right tool and learn how to use it to make my idea become something (even if it doesn't get finished). When that purpose or desire disappears (for whatever reason) I stop wanting or caring about learning more about the tool I was using to do it with.

Your initial request seems to point to a different style of learning, wanting to do it for the journey itself. That's cool, I just wonder if you had a reason for doing it, would it make the effort more fun and worthwhile.

Kubernetes (ala k3s) you can make any collection of computers a cluster and play with automation of apps and services

KiCAD play with circuit board design with FOSS.

FPGA programing! Tons of use case for when you need near line speed but can't afford the time and money it takes to build a full ASIC.

idk the software but multitrack audio editing sounds fun.

One thing I want to learn which seems important to me career wise is HEC-RAS, a hydrological River Analysis Software. I think it's free?

From this you can build your own predictions of when flooding (or drought!) will occur in your local area

Get your finances in order with Firefly III and Waterfly III (Android app, available in F-Droid)

Use graphviz dot files to draw a graph

Draw some graphs from data files downloaded from public university data sets in GNU Octave

Write a review of the process and tools with embedded images and code in LaTeX

CRRCSim (RC plane simulator)

Learn how to slope-soar a glider.

Best with the photo mountain scenery added in.

In many distro repositories too.

https://github.com/gcmcnutt/CRRCsim

Obsidian (Free but not OSS) and PKM. Might help you improve how you build your knowledge, or might just trap you in an endless hunt for the perfect system.

NixOS if you’re looking for an endboss kinda thing.

Try Proxmox Virtual Environment with community post-install scripts. It's a little virtual data center that you install on a dedicated small PC. You can run all kinds of services like a Linux VM, Pi-Hole, Copyparty, Romm, and stuff. It'll make ![email protected] very happy.

Python, and you kind of want to take the long way around.

Get it up and running in its own virtual environment. On Linux and Windows this'll just be a directory its in, and once you've activated that install via a terminal command everything stays self contained. It has a package manager called "pip" that will handle package and dependency management. Use pip to install spyder, pandas, matplotlib, numpy, scipy, and openpyxl. If you install anaconda this is what it's doing under the hood, but there are licensing hiccups with using their package repos.

Anyway, however you get up and going, numpy is fast numerical storage, scipy is a lot of scientific algorithms, pandas is a data analysis library that rides on top of numpy, and openpyxl is an interface to excel files from python. Pandas will get you one line CSV file reads and writes and more complex manipulation of Excel spreadsheets. Openpyxl gets you cell by cell manipulation of a spreadsheet. Spyder is a development environment.

It can do much, much more.

I asked an LLM for a small python example with pandas and matplotlib. Load it into spyder and run it and see what happens (tip, go into the settings/preferences, IPython Console, Plotting, and change the Graphics Backend to "Qt" to get the plots in their own window). ::: spoiler Python Example

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

def generate_damped_signal():
    # 1. Setup Parameters
    fs = 50                 # 50Hz Sampling frequency
    t_max = 6.0             # Run for 6 seconds to clearly visualize it hitting 0 at 5s
    freq = 2.0              # Oscillation frequency in Hz
    
    # 2. Generate Independent Time Axis
    # 50 samples per second from 0 to t_max
    time = np.arange(0, t_max, 1/fs)
    
    # 3. Generate Dependent Damped Signal Axis
    # Using an exponential decay constant of 1.0 ensures that at t=5 seconds,
    # e^(-5) drops down to ~0.006, effectively decaying the signal to zero.
    amplitude = np.exp(-time) * np.cos(2 * np.pi * freq * time)
    
    # 4. Create Pandas DataFrame
    df = pd.DataFrame({
        'Time_Seconds': time,
        'Signal_Amplitude': amplitude
    })
    
    # 5. Export DataFrame to CSV File
    csv_filename = "damped_signal.csv"
    df.to_csv(csv_filename, index=False)
    print(f"Successfully generated DataFrame and saved to '{csv_filename}'")
    
    # 6. Plot the Data Using Matplotlib
    plt.figure(figsize=(10, 5))
    plt.plot(df['Time_Seconds'], df['Signal_Amplitude'], label='Damped Signal', color='cyan', linewidth=2)
    
    # Visual Anchors for the 5-second decay mark
    plt.axvline(x=5.0, color='red', linestyle='--', alpha=0.7, label='5-Second Decay Target')
    plt.axhline(y=0.0, color='gray', linestyle='-', alpha=0.5)
    
    # Labeling and Grid Configuration
    plt.title('Damped Signal Decay Over Time (50Hz Sampling Rate)')
    plt.xlabel('Time (Independent Axis - Seconds)')
    plt.ylabel('Signal (Dependent Axis - Amplitude)')
    plt.grid(True, linestyle=':', alpha=0.6)
    plt.legend()
    
    # Display the Plot Window
    plt.show()

if __name__ == "__main__":
    generate_damped_signal()

:::

Emacs! Emacs Makes All Computing Simple.

GIMP

AI image editing can only go so far.

Learn the basics of accounting by trying to use GnuCash (or KMyMoney) for your personal finances.

Or learn a proper text editor, such as vim.

KiCad takes around 5 minutes to learn and is some of the best software for designing schematics and PCBs.

Falstad is great for when you need simulations of schematics and don't want the headache of trying to use KiCad's built in simulation tools.

Both are FOSS.

wow rekordbox looks nice! I've used Mixxx up til now.

One killer feature might make me switch: I see rekordbox allows mixing of spotify or apple music songs: do they also support navidrome? That would blow me away!

about the topic: what about home assistant? That should prove an adequate rabbit hole for you :)

I learned a decent bit about how biometric authentication works (or at least this specific implementation) by installing, setting up, and tweaking settings for Biopass. I also learned about how when you do first login using this method, it can fail to unlock keyrings because the password authentication has been bypassed so no password has been provided to unlock the keyring. It includes anti-spoofing local AI models, and the dev plans to have the option for the user to download and use any model for anti-spoofing/recognition. Interesting stuff.

https://github.com/TickLabVN/biopass

Slackware- Wait you said fun, nvm

Aseprite (you gotta compile it yourself if you wanna it free tho)

:wq!

I recommend learning dc if you don't already know it, and either Octave or Python.

https://en.wikipedia.org/wiki/Dc_%28computer_program%29

ZK https://github.com/zk-org/zk

Install one of the distributions where you have to do most of the installation steps manually, such as Gentoo or Slackware or Arch. Or Linux from Scratch of you want hardcore mode.

sunvox

PosteRazor, is super easy to learn.

It can make wall posters, by printing the A4 segment sheets, and then gluing them together.

https://posterazor.sourceforge.io/

Make sick beats with milkytracker.

I honestly have that still on my to-learn list myself. But it does seem to be a solid choice for FOSS trackers.

i've been hitting up kaggle.com, freecodecamp and exercism.org for Python courses.

Selfhosting is a nice rabbit hole

Nushell

Blender

Godot

I saw Krita was already suggested. Also give Inkscape a go. It's meant for vector graphics instead of raster. (like SVG vs jpeg).

Since you already recorded something with OBS, you could try your hand at video editing with something like kdenlive

Schism Tracker

Link to user manual

Prompting claude for python scipts you feed into FreeCAD to build 3d models, dimensional drawings and for everyhung you coild ever imagine.

Inkscape