"Sia is the leading decentralized cloud storage platform. No signups, no servers, no trusted third parties. Sia leverages blockchain technology to create a data storage marketplace that is more robust and more affordable than traditional cloud storage providers."

You 'rent' space on users' unused storage and it gets saved with 3x redundancy in decentralized, encrypted blocks. Sounds interesting and is pretty cheap (~$4 per TB) so could be something to look into more