ZoneDetect:  BSD-3-Clause License 
https://github.com/BertoldVdb/ZoneDetect

This is a C library that allows you to find an area a point belongs to using a 
database file. A typical example would be looking up the country or timezone 
given a latitude and longitude. The timezone database also contains the country information.

download the database files:
  https://cdn.bertold.org/zonedetect/db/db.zip

out/timezone16.bin
 - Contains data from Natural Earth, placed in the Public Domain. Contains
   information from https://github.com/evansiroky/timezone-boundary-builder,
   which is made available here under the Open Database License (ODbL).