OSM Buildings also provides from alternative open data sources which are subject to their repective licenses. These sources are not part of and not connected to OpenStreetMap.
OSM Buildings uses Nominatim for search and geocoding.
OSM Buildings viewers's source codes are open and free to use for everyone as long as copyright notice / attribution is attached.
We are also using Mapbox GL for demonstration of our vector tile service. The viewer is copyrighted by Mapbox.