Many applications require geographic coordinates for given addresses. The process of finding coordinates for an address is called geocoding. More and more, OpenStreetMap data is used for such geocoding. There's a piece of free software that does an excellent job at this, and it is called Nominatim.
OpenStreetMap is still quite a bit away from having complete house number coverage in most countries. Of course, the geocoding accuracy is limited by the precision with which streets, houses, and their house numbers have been recorded in OpenStreetMap. Coverage of house numbers is usally very good in urban areas of Europe. In other areas, geocoding is usually possible on street level only.
The precision currently offered by OSM is sufficient for many use cases. Geofabrik does not run their own Nominatim server, but we offer to install such servers for clients, either on their own hardware or on hardware leased by us, or we help clients to install Nominatim themselves.