NBIB is the National Library of Medicine's citation format for PubMed exports. Structurally identical to RIS with a different tag dictionary (PMID, FAU, JT, AID instead of ID, AU, JO, DO). Reference managers treat .nbib files as RIS-flavored with PubMed-specific extensions. The format ships with PubMed downloads and the major systematic-review tools (Covidence, Rayyan).
How to open
Zotero, Mendeley, EndNote, Papers, all read NBIB natively. Plain text in any editor.