Data sources
Kaufabsichten shows places and maps with open data from these sources.
Postal codes
Postal code locations: GeoNames (geonames.org), CC BY 4.0, averaged per postal code.
Maps
Map tiles: OpenFreeMap, © OpenMapTiles, data from OpenStreetMap.
Each map credits them in its corner as well.
Address search
Powered by Geoapify · © OpenStreetMap contributors
Credited beside the address field as well.