ResearchGate is described as 'Connects scientists to share papers, datasets, and findings, discover global research, track publications, and engage in scholarly discussion within a scientific network' and is an app in the education & reference category. There are more than 25 alternatives to ResearchGate for a variety of platforms, including Web-based, Windows, iPhone, iPad and Android Tablet apps. The best ResearchGate alternative is Mendeley, which is free. Other great apps like ResearchGate are Google Scholar, WorldCat, Academia.edu and ResearchCollab.
A great quantity of papers with most papers being free