Open-source systems help to manage the rapid development of software, while governing open-source systems properly can effectively promote software and software engineering. However, some significant problems, such as code controls, incentives, interaction and cooperation, automation, transparency and fairness of rights and responsibilities, cannot be properly solved by traditional methodologies. The decentralization, immutability, change in trust mode and smart contract programming of blockchain provide new solutions. In order to solve the problems of traditional centralized open-source governance, this paper proposes a decentralized open-source coordination management system using a novel triple-blockchain architecture. Through the analysis of traditional and blockchain-based research, the business and technical issues that need to be addressed in decentralized open-source governance systems have been emphatically studied. Combined with triple-blockchain architecture, smart contracts, oracles and continuous integration tools, we study the decentralization of open-source businesses and make them more trustworthy, automated and coordinated. An identity authentication mechanism is designed for permission control and inter-community collaboration. A decentralized open-source reputation is proposed for incentive and reference. We also improved the DPoS (Delegated Proof of Stake) consensus under triple-blockchain architecture to reduce repeated elections. By constructing the OSCMS prototype based on the proposed architecture model, many comparative experiments were conducted under different parameters and conditions and showed good feasibility, scalability, reliability and performance. The OSCMS not only solves the shortcomings of previous research but also provides a comprehensive and feasible reference for the decentralized practice of open-source governance.