Flopp’s Map is entirely built on open source software; you can have a look at the implementation and even participate in the development over at Github. Everything is customly developed in TypeScript.
The following libraries/projects are used:
Leaflet is used as the basic mapping library; in the past, Flopp’s Map was based on the Google Maps API – but this had to be ditched due to problems with Google’s terms of sevice.
Geographiclib provides geographic calculations (calculating distances, performing waypoint projections, etc.).
For geocoding (location search), Nominatim is used.
The website is hosted at Uberspace.