After connecting my iPhone to EOS, two discoveries:
converseen converts between a lot of image formats using a simple GUI; in particular, it takes care of the annoying HEIC image format which Apple likes.
exiv2 -d a <image> removes all metadata from an image (despite the command name, not just EXIF format). exiv2 has a ridiculous number of options.
And another two. I am a strong chess player, and chess programs on Linux have always been a bit of a problem - there are a lot of old programs around and, especially, those with outdated GUIs.
However, there are two little-known, excellent ones outside the repositories (not in the AUR):
Both install into ~ (no root access).
The first has an insane number of bundled chess engines and an an almost as insane degree of customisation, but sensible defaults.
The second requires more knowledge of the ins and outs of chess engines, but is also very good.
Try Stockfish chess program. Let me if you can beat it!
sysctl on steroid 
Quite unlike Schism Tracker or other one which leans heavily toward wave-file samples.
I also picked up AdlibTracker 2 SDL but it’s 32-bit only. It looks like a terminal program, it looks like it was originally written for Windows. Currently running it on one of the Debian descendants. Like the kewl FM sounds from music without audio effects applied!
Bummer that on Furnace one has to “pick” the type of FM chip. Because on “Sega Genesis” default mode each SB1 file that I load does the same noisy useless sound. 
I imported the ones that came with the other program.
LOL maybe that’s why Slackware comes with two of them, one which seems to be the newer release of the other? I didn’t bother with that “XBoard” anyway…
XBoard is ancient - not only does it look outdated, it uses an outdated protocol for communicating with chess engines. But, as you say, it clings on.
At least Lucas Chess and Banksia are modern - they are regularly updated, written with up-to-date toolkits (Qt) and know about new concepts like LC0.
I can if I reduce the rating it plays at to 1800 
That option, which is also in Komodo 13, makes chess programs relevant again. Even Carlsen would be crushed by Stockfish without a rating reduction …
“rm” but safer 
scid-vs-pc chess interface is good with stockfish or any other chess engine.
The thing is that Stockfish is used also to do chess analysis. when you watch chess tournaments like Tata Steel they have Stockfish running that gives suggestions on the best move for a position.
For Wallpaper lovers:
Been using Joplin for note taking so I can remember some of the more complicated things in Linux.
nvtop is a nice top-like cli tool that shows which apps are using your Nvidia GPU and also shows you frequency, memory use, etc.
I wanted to have a noteapp when I moved to Linux about 2 years ago and my friend threw Obsidian.md into the mix.
I haven’t been able to understand how I could live my life without a note app before that point.
It does use electron which is shit but I’ve never had an issue with Obsidian despite this.
Syncthing
I started using this amazing app to sync my photos and markdown notes between my phone and PC.
i was looking for an app like this since i got my first phone about a week ago, is this better than kde connect ?
Dunno, I haven’t tested KDE connect, but I think Syncthing is more universal because it is not only for mobile devices.
I have discovered NightPDF … it’s nice application you can find here
This application helps to save your eyes while opening a pdf file
…
it’s simple application you can download as an appimage or making a compilation with the git clone option !
Conjure - a GUI for ImageMagick
for someone like me who prefers to work with gui than terminal a great tool
Auf Deutsch - gefunden bei gnulinux.ch