QGIS - QGIS is a desktop geographic information system, or GIS.
ipstack - ipstack is a free, real-time IP address to location JSON API and database service supporting IPv4 and IPv6 lookup.
GRASS GIS - GRASS GIS is a free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization.
ipapi - Web analytics with IP address lookup and location API
SAGA GIS - SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS)...
ipgeolocation.io - Free IP Geolocation API and Accurate GeoIP Lookup Location Database