[jraph]

It exists :-)

For zip archives, there are fuse-zip and mount-zip which are FUSE filesystem.

As an intermediate between OS level and application-level, there are desktop environment level: gvfs for GNOME and KIO for KDE, but they are compatible only in their own ecosystems.

[lambdaxyzw]

Would be nice to have something that integrates with 7z - it supports a lot of weird archive types, including "weird" ones I care about (for example PE files, better known as ".exe files").

[russfink]

Or zstd. I have some dd blobs of partitions, the blobs are zstandard-compressed, would like to mount them.

[mxmlnkn]

Ratarmount also works for that. However, it, and any other tool I know of, works only well if it was compressed with pzstd because of a limitation of the zstd format. It needs separate zstd frames for fast seeking.

[ramses0]

ratarmount for tar files.