Developing software for OpenStreetMap data all starts with the PBF - it’s nodes, ways and relations in the raw, native OSM format. You can make tiled maps, PostGIS databases, or GeoJSON out of PBFs, but those conversions lose some tagging and metadata. With PBF, you get pure OpenStreetMap! The global OSM.org website provides a weekly copy of the entire planet as one ~80GB PBF. And there’s convenient sites like Geofabrik Downloads for getting just one country of data.
