Here are some identifier services listed as such by FIP Wizard, a free-to-signup online tool to guide a user in creating and publishing a machine-actionable FAIR Implementation Profile (FIP): Old IGSN International Generic Sample Number before integration with DataCite SDN CDI PID | SeaDataNet CDI PID SeaDataNet Common Data Persistent Identifier U.S. Department of Energy Office of Scientific and Technical Information (OSTI) Data ID Service