I'm an engineer on Mapbox's search (geocoding) team, and our geocoding engine is actually open source: https://github.com/mapbox/carmen https://github.com/mapbo

I'm an engineer on Mapbox's search (geocoding) team, and our geocoding engine is actually open source: https://github.com/mapbox/carmen https://github.com/mapbox/carmen Our data isn't, but as other commenters here have said, it's not currently possible to build a good geocoder with the open data available. We're constantly working to support open data efforts, but it's not there yet.