Lots of good answers, especially using FUSE for experimentation. One thing I’ll add is that if you just didn’t want to use any filesystem at all … you don’t have to!

At least in the Unix realm, a disk drive is just a bunch of contiguous blocks, and you can put whatever you want in them. Of course, Unix itself famously needs a filesystem for itself, but if you want to just store all your giant binary blobs – cryptocurrency block chain? – directly onto a drive without the pesky overhead or conveniences of a filesystem, that’s doable.

It’s not generally a useful idea to treat a disk drive as though it’s a tape drive, but it does work. And going further into that analogy, you can use “tar” to collect multiple files and fit them onto the drive, since a tarball preserves file metadata and the borders between files, but not much else. This is the original use of tar – “tape archive” – for storing Unix files onto tape, because the thought of using tape as working storage with a filesystem was – and still is – a terrible idea. And that’s basically the original impetus for a filesystem: it’s better than linear access media.