"GNUnet is a framework for secure peer-to-peer networking that does not use any centralized or otherwise trusted services. A first service implemented on top of the networking layer allows anonymous censorship-resistant file-sharing. GNUnet uses a simple, excess-based economic model to allocate resources. Peers in GNUnet monitor each others behavior with respect to resource usage; peers that contribute to the network are rewarded with better service.
GNUnet is a peer-to-peer framework with focus on providing security. All peer-to-peer messages in the network are confidential and authenticated. The framework provides a transport abstraction layer and can currently encapsulate the network traffic in UDP (IPv4 and IPv6), TCP (IPv4 and IPv6), HTTP, or SMTP messages. GNUnet supports accounting to provide contributing nodes with better service. The primary service build on top of the framework is anonymous file sharing."
Note: GNUnet acts as a Friend-to-friend network when it's F2F topology is enabled.