GitHub is a service to help software developers. It uses Git for revision control and source code management. GitHub offers 2 plans: a paid plan for private projects and a a free plan for open source projects. There are also social networking aspects including feeds and following that allows developers to collaborate.
ResearchGATE is social networking platform for scientists and researchers. It is Facebook for scientists. Although it focuses on science, it is open to many other disciplines. ResearchGATE is a repository and discovery tool containing thousands of articles and millions of abstracts. Scientists can create profiles, discover collaborators, upload articles, discover articles, find jobs, and discuss their work. ReseardhGate is free of charge
A site for questions and answers related to programming and computer science.