The modern official tabletop game, by Modiphius Entertainment, offers several free digital resources:
Various versions (like 1.1 or 2.0) of these community-made rulebooks can be found on document-sharing sites like Scribd or Internet Archive . download-fallout-the-games-download-zip
A collection of lore and early design documents for a Fallout 3 project (Van Buren) that includes early pen-and-paper testing notes, often hosted as a PDF on sites like GOG. Fallout: The Roleplaying Game Downloads The modern official tabletop game