QGIS Nominatim Locator Filter Plugin
This is a so called QgsLocator filter for the Nominatim/OpenStreetMap search service, implemented as a QGIS plugin.
Read about writing one here:
This Locator Filter searches for names in the Nominatim service:
You can install this 'Locator Filter' as a plugin by searching for it in the QGIS plugin manager in your QGIS desktop, search for 'Nominatim':
Some more docs and api's: