It already exists... sort of.
Cataclysm: Dark Days Ahead. Zombie survival roguelike, forked from the original cataclysm by whales. Also check out Cataclysm: Bright Nights which is a fork of CDDA that makes it more gamey like the original, and less like you're playing 2d arma.
Powering the laser takes 300 MJ but the actual laser power (the energy in the light) is only 2.05 MJ. The rest of the energy is lost to heat and other inefficiencies. If the laser could be created with 100% efficiency then the input energy would also be 2.05 MJ.
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
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.
"Trust me."
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)
To be clear, that's Cataclysm:Dark Days Ahead or CDDA. It's quite removed from the original cataclysm by whalesdev, and is more focused on strict realism. There is also Cataclysm Bright Nights which is closer to the arcadey feel of the original. Both are great and are open source.