We present an application-level implementation of anycast for highly dynamic groups. The implementation can handle group sizes varying from one to the whole Internet, and membership maintenance is efficient enough to allow members to join for the purpose of receiving a single message. Key to this efficiency is the use of a proximity-aware peer-to-peer overlay network for decentralized, lightweight group maintenance; nodes join the overlay once and can join and leave many groups many times to amortize the cost of maintaining the overlay. An anycast implementation with these properties provides a key building block for distributed applications. In particular, it enables management and location of dynamic resources in large scale peer-to-peer systems. We present several resource management applications that are enabled by our implementation