ORCID provides a unique digital identifier (an ORCID iD) that the account holder owns. This ID site hosts the account owners' professional information; affiliations, grants, publications, peer review. The ID can be used to share information with other systems, ensuring recognition for all a user's contributions, saving time, and reducing the risk of errors.
A Google Scholar profile is a very simple way of hosting your publications (and citations to them) so that others can find your work. You can choose automatic updates so that your publications list will populate automatically when you publich something new. Google Scholar profiles improve the page rankings for profile owners.
ResearchGate is a professional network for scientists and researchers. Over 17 million members from all over the world use it to share, discover, and discuss research. It's mission is to connect the world of science and make research open to all.