Building a Black Net (Peer to Peer-like Network) with Participant Anonymity or Plausible Deniability

Question

How would you programmatically design a "black net" where peer to peer-like data exchange (file transfer, chat etc) is possible but the anonymity of the seeder/sender(s) is either entirely hidden or at least all participants have 'plausible deniability', meaning their exact involvement and/or knowledge of transactions or activity on the system can't be proven beyond any reasonable doubt?

Answer 1

There's a large number of these around (here's a link to a list), many of them OSS. You might be able to leverage design information from some of these.