Nominatim (from the Latin, by name) is a tool to search OpenStreetMap (OSM) data by name and address and to generate synthetic addresses of OSM points (reverse geocoding).
Geocode
Census.gov
The Census Bureau’s mission is to serve as the nation’s leading provider of quality data about its people and economy.
Azure
Azure is an ever-expanding set of cloud computing services to help your organization meet its business challenges. With Azure, your business or organization has the freedom to build, manage, and deploy applications on a massive, global network using your preferred tools and frameworks.
IPStack
Locate and identify users by IP address.
Geocodio
Straightforward and easy-to-use geocoding, reverse geocoding, and data matching for US and Canadian addresses.