I am looking for a service that lets me use geolocation autocomplete functions like ng4-geoautocomplete , which looks awesome and works perfectly, but works with google maps API.
Is there something similar, where you dont have to register for an Google API Key, like a library based on Open Street Maps?
Take a loot at Nominatim OSM
"Nominatim is a search engine for OpenStreetMap data...", for more details, check this link https://nominatim.openstreetmap.org/
Also check this article out leaflet-and-nominatim, here you can find a good example of using Nominatim with Leaflet. This example based on jQuery, but the main concept for Angular framework will be the same.
Hope this will help you :)