I created this to solve my own need for reverse geocoding: https://github.com/punnerud/rgcosm (Saving me thousands of $ compared to Google API)

Uses OpenStreetmap file, Python and SQLite3.

First it finds all addresses using +/- like a square from lat/lon, then calculate distance based on the smaller list (Pythagoras), and pick the closest. It expands until a set maximum if no address is found in the first search.