ORCID
ORCID (orcid.org) is an independent identifier, not linked to any one service. Identifiers are controlled by the researcher, who decides what information is displayed and what publications are associated with it. It is used to associate papers with authors in Scopus and Web of Science, and a growing number of publishers now request it when a paper is submitted, so that the identifier can be embedded in the metadata. For more information and to register, please refer to the right-hand column.
The identifier automatically creates a profile page at the ORCID site, but the researcher controls what (if any) publications or metadata are displayed. No metrics are shown.
Scopus
Scopus identifiers are automatically generated by the Scopus publications database and used to link papers by the same author or to browse within the database. The researcher does not directly control these records, but they (or a third party) can submit corrections or request that two records be merged (more details). It can be associated with an ORCID identifier.
The identifier automatically generates a profile page in Scopus, with a list of publications and some associated bibliometrics.
ResearcherID (Publons)
ResearcherID is a service offered by Clarivate (Web of Science). It was closely integrated with Web of Science, and the identifier could also be used to search within Web of Science.
As of April 2019, ResearcherID was integrated into Publons, another Clarivate tool that enables authors to track their peer-reviewing activity. (Existing ResearcherID numbers remain linked to Publons accounts, but no new IDs can be registered). A Publons account offers similar functionality for displaying a user profile and some bibliometrics, but does not provide an identifier for searching within the Web of Science.
Google Scholar
Google Scholar offers a "profiles" service, which allows a researcher to control and curate a publications list on Google Scholar. It requires an existing Google account, and profile pages are only created if the researcher opts in.
The profile lists all publications, along with relevant bibliometric data. (See some examples of University of Warwick researchers with Google Scholar profiles.)