Cep.la
Brazil RESTful API to find information about streets, zip codes, neighborhoods, cities and states

Open APIs for select European cities.
CitySDK API is a free Geocoding API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Discover CitySDK, a development kit that harmonizes APIs for cities and developers, facilitating the creation of innovative applications to improve participation, mobility and tourism. A European collaborative project since 2012.
Details from citysdk.eu.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Brazil RESTful API to find information about streets, zip codes, neighborhoods, cities and states
World countries, states, regions, provinces, cities & towns in JSON, SQL, XML, YAML, & CSV format
Convert British OSGB36 easting and northing (British National Grid) to WGS84 latitude and longitude
The CitySDK API is provided by CitySDK (citysdk.eu). Discover CitySDK, a development kit that harmonizes APIs for cities and developers, facilitating the creation of innovative applications to improve participation, mobility and tourism. A European collaborative project since 2012.
Yes. The CitySDK API is listed in the Geocoding category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The CitySDK API requires no authentication, so you can start making requests without signing up.
CORS support for the CitySDK API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The CitySDK API is served over HTTPS, so it's safe to use in production.