With the acceleration of urbanization, the demand of high quality public services has been increasing. In the past fifteen years, each department of Chinese government has established its own information service system to provide public services to people. However, these systems are isolated from each other and the services they have provided are not well organized. To tackle this problem, this paper proposes a novel platform for the service management and application development in smart cities. Based on this platform, different people can collaborate and make their contributions, such as requirement acquisition and service development. First, we gather all information and services from existing system to the platform. Second, the platform can publish application or service development requirements based on the crowdsourcing paradigm. Third, small-to-medium service vendors and developers could undertake these development tasks and make use of services provided by our open platform to develop innovative applications. Finally, it provides human-centered services to citizens in appropriate channels when necessary. In this paper, we present the architecture design of the platform and key technologies to implement it. Besides, two practice cases in smart cities of China are given to demonstrate the effectiveness of the platform.