If doing an overlay network (network on top of the Internet), you probably won’t be able to do much better than Tor or i2p.

We confirm the trilemma that an AC [anonymous communication] protocol can only achieve two out of the following three properties: strong anonymity (i.e., anonymity up to a negligible chance), low bandwidth overhead, and low latency overhead.

freedom.cs.purdue.edu/projects/trilemma.html

This applies to all types of anonymous networks as well (BT, Wifi, etc).