Rhubarb is a platform for building peer-to-peer (P2P) applications. Rhubarb offers an API similar to Berkeley sockets. Using Rhubarb, P2P applications can be developed that are independent of centralized resources and the DNS system. Rhubarb organizes nodes in a virtual network, allowing connections across firewalls/NAT, and efficient broadcasting. The virtual network is scalable due to a hierarchical organization and efficient state management. Rhubarb is securely protected against outside and inside attacks.