Easta is a Napster-inspired peer to peer filesharing system, built to
operate entirely over email (POP/IMAP+SMTP). More people have access to
email than any other service, and in addition it gives easy access to
file-sharing for the 90% of the planet stuck behind a firewall without a
SOCKS connection. There's some nice side-effects too, such as asynchronous
downloading, even when you're offline.