Network Data Labs
IP geolocation with accuracy radius, ASN, and flags for Tor exits, known VPN networks and hosting
Provides worldwide forward / reverse geocoding.
Nominatim API is a free Geocoding API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Details from nominatim.org.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
IP geolocation with accuracy radius, ASN, and flags for Tor exits, known VPN networks and hosting
The Nominatim API is provided by Nominatim 5.3.3 Manual (nominatim.org).
Yes. The Nominatim 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 Nominatim API requires no authentication, so you can start making requests without signing up.
Yes. The Nominatim API supports CORS, so front-end JavaScript can call it directly.
Yes. The Nominatim API is served over HTTPS, so it's safe to use in production.