Anomos

Anomos is a pseudonymous, encrypted multi-peer-to-peer file distribution protocol. It is based on the peer/tracker concept of BitTorrent in combination with an onion routing anonymization layer, with the added benefit of end-to-end encryption. By combining these technologies, we have created a platform where by no party outside of the trusted tracker will have any information about who a peer is or what they are downloading.

Anomos is designed to be easy to use - you won't even be aware of the security that it provides. Anybody who is already familiar with BitTorrent won't have to do anything differently, other than use 'atorrent'
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Requirements

Mac OS X 10.5 or later