We describe MutualCast, a serverless peer-to-peer (P2P) multiparty real-time audio conferencing system. In MutualCast, the peers form a fully connected clique. During the conferencing session, each peer takes turn to mix and redeliver the compressed audio. The audios are split into frames, and the number of frames mixed and redelivered by a certain peer is proportional to the available resource of the peer, e.g., the upload bandwidth or the computation power. MutualCast balances the serving load (network bandwidth and computation power) needed for the mixing among all participant peers. It enables a multiparty conferencing session without any powerful server.