PubMed & Its Predecessors
The National Library of Medicine has been collecting and organizing citations of biomedical literature since its founding. For more on the history of these systems, see the articles below.

IBM 370/155 master console (right) and high-speed printer (left) with NLM staff
Source: The development of the Medical Literature Analysis and Retrieval System (MEDLARS). Journal of the Medical Library Association, 95(4), 416–425. http://doi.org/10.3163/1536-5050.95.4.416