A while ago, this guy found that you could store files in the DNS servers belonging to other people, and created DNSFs that he documented here: https://blog.benjojo.co.uk/post/dns-filesystem-true-cloud-st...

It looks like there might be about 250mb available for all to share across the internet using this system

PingFS is even more out there!

The internet is full of weird corners to exploit in fun ways

Free yes but they come with an energy tag on it. (backup and redundant systems etc). I wonder how much energy it would take to store it like this compared a local hard drive and simple PC or Raspi.