It's not exactly what youre describing, but isnt e-Mail a decentralized file store? Sure, most mail is google, microsoft, or verizon by now, but still, you can

It's not exactly what youre describing, but isnt e-Mail a decentralized file store? Sure, most mail is google, microsoft, or verizon by now, but still, you can spin up your own compatible instance and participate with others. Almost any client you can dream of can access IMAP mailboxes and send through SMTP.