Ask HN: Unusual UIs using computer-computer metaphors, like fake filesystems?

A lot of computer UI things, if not most, use real-world metaphors, like windows, files, folders, buttons, paste etc, but I'm asking about metaphors between two computer domains, like a folder representing a youtube search (ytfs), or a text file representing a wikipedia page (WikipediaFS) etc.

What are some other UI ideas, using system features for unintended purposes, that you've come across or thought of? Using our familiarity with one domain in another, in a surprising/neat way, so tools meant for one domain can be used elsewhere? Thank you.

(I'm sure "computer-computer metaphors" isn't what these things are called! I'm not sure what to search to learn more.)

Synthetic file systems (deriving from Unix's 'everything is a file/stream of bytes'?) are one common example of this, as are virtual memory/addresses and virtual machines.

Omar Rizwan's talk at !!Con 2018, Four fake filesystems!, started me thinking about this.