The scale-free network shown in the small world phenomenon indicates that our human society consists of a small number of people who play the role of hubs linked with many nodes (persons) and a large number of people as nodes linked with few nodes. From our analysis of a large-scale online community - SourceForge.net - which has a large number of developers and projects, we have found that SourceForge also exists as a scale-free network. That is, only a minority of developers joins many projects and has rich links with other developers, while the majority joins few projects and has very limited social relations with others. The goal of our study is to build a system that supports knowledge collaboration in a large-scale online community of software development projects. In this paper, we discuss the challenges of supporting knowledge collaboration in such a large online community that is a scale-free network and then introduce the prototype system called D-SNS (dynamic social networking system).