zbMATH Open (formerly known as Zentralblatt MATH) is the world's most comprehensive and longest-running abstracting and reviewing service in pure and applied mathematics. It is edited by the European Mathematical Society (EMS), the Heidelberg Academy of Sciences and Humanities, and FIZ Karlsruhe.
Project Euclid is jointly managed by Cornell University Library and Duke University Press. It was originally created to provide a platform for small scholarly publishers of mathematics and statistics journals to move from print to electronic format.
Hosted by the American Mathematical Society, this "bibliographic index of publications in statistics, probability, and related fields. It includes data from approximately 160 core journals, 1,200 additional journals in related fields, and 11,000 books. The bulk of the content in CIS is from 1975-2017."