You have to add them manually, either by url or with the built in search. For example, you can add newpipe by searching sources and checking github as a source to search. It will then show you repos that match newpipe, which usually is the regular newpipe repo and then a bunch of forks of it.

Obtainium isn’t for finding FOSS apps, it’s for installing them. To find them, you can check out existing repos such as f-droid or izzy, or you can ask around. This post has a bunch of recommendations in the replies

Obtainium lets you install FOSS programs directly from the developers source. You can get updates from the github/gitlab of app developers before they get uploaded to F-droid.

Hyperrogue is not quite a top down hexagon world, it’s a top down heptagon world. The premise is that it is a roguelike set in a hyperbolic world, and different regions teach you different weird properties of a hyperbolic space. For example, the crossroads feature an infinite amount of parallel lines and yet there are still forks in the pathway.

Even though it’s foss, it is also for sale on steam if you want to support the dev

Lossless Cut FOSS, Crossplatform frontend for ffmpeg. Note that to do it losslessly, it will still be in mp3. If you need to transcode you can do that too, but like others have said you’ll probably lose quality.

If you really don’t want to spend money, there’s always GNU Octave. Sure, it doesn’t have the thousands of matlab toolboxes, but if you’re running code from 40 years ago it shouldn’t need those anyway. I wrote a couple of scripts recently and then rewrote them slightly so that they would be compatible with octave.

Puzzles (40 single-player logic games) I recommend this package on f-droid for puzzles. As for an organised list, f-droid is pretty lacking in terms of subcategories within it’s categories, but I have skimmed that whole category a couple times just to see if anything is interesting. There is also a solitaire package in there. Simple Solitaire Collection (Solitaire game collection with 17 games)

The monoblock was a prototype watercooling block that interfaced with the cpu and gpu simultaneously. Normally if you wanted to watercool both components one would purchase seperate waterblocks for the cpu and gpu and then use plumbing in between the two.