I had a project in college (~2007-2008) for this! My project partner and I set up a sharded filesystem using gmail account storage, storing metadata in the title and splitting encoded chunks across emails and accounts. The storage limit per gmail acct was in GB, but the attachment limit per email was ~20mb. We spent quite a few nights figuring out bugs in our algo to stitch together major and minor chunks of string-encoded binaries.

Once the cloud storage companies launched and provided free/cheap tiers for huge storage we mostly lost the need for it.