Peer-to-Peer (P2P) computing, the harnessing of idle CPU cycles through the Internet, offers new research challenges in distributed computing. One of the most critical aspects in the design of P2P systems is the development of incentive techniques to encourage cooperation and resource sharing among participants. To tackle this problem, in this paper we propose an incentive and scheduling mechanism based on credits with a two-level topology which is designed to operate on different types of shared computing networks, such as P2P, P2P Grid, Opportunistic Grid, Desktop Grid, volunteer computing platforms, among others. The low level association of peers is made up of one super-peer and its constituent peers. The main contribution at this level is a new reinvestment policy, called ‘‘Weighted’’, that increases peer participation significantly. This mechanism reflects P2P user dynamics, penalizes free-riders efficiently and encourages peer participation. Scalability limitations on the first level are avoided by providing the mechanism with an upper level, made up of super-peers interconnected through an upper level overlay. Our main contribution at this level is the proposal of a task scheduling policy based on three criteria, computing capacity with neighbors, distance and reputation that only use local information for mapping tasks. Simulation results show our proposal performs well and is functional.