Once we had to ship millions of extremely small files to our customer, we ended up throwing them into a MongoDB and serve them with a web server. It worked great.
We tried to use an image of traditional filesystems (ext4 and fat32), but with most files being under 1 KiB, it was super wasteful.
The way our "MongoFS" was organized is actually also low quality and probably would fall apart pretty quickly if used as a serious web service. However, it works if you try to quickly deploy and serve millions of files to a small number of clients.
Our use case was a Maven mirror for disconnected environment that only contains metadata (i.e. lots of small XML files, without the actual jar). We already had a MongoDB service for some other JSON data, so here we are.
We tried to use an image of traditional filesystems (ext4 and fat32), but with most files being under 1 KiB, it was super wasteful.