The File Filesystem (2021)

Useful enough that it should be an OS-level standard feature, imho.

Unix-like OSes allow mounting disk images to explore their contents. But there's many more file formats where exploring files-inside-files is useful. Compressed archives, for one. Some file managers support those, but (imho) application-level is not the optimal layer to put this functionality.

Could be implemented with a kind of driver-per-filetype.

This was a core design feature of reiserfsv4, but Linux ultimately refused to merge it, probably not helped by the whole murdering-his-wife thing.

> This was a core design feature of reiserfsv4, but Linux ultimately refused to merge it

IIRC, because it contained these strange beasts which functioned as both files and directories - i.e. cat would return data, but then you could cd into them and run ls. Linus (among others) didn’t want to permit those violations of the file-directory dichotomy into the Linux kernel.