Graphhopper VS JTS Topology Suite

Well I think what he means is that we dropped the explicit support of Android and the example app with offline maps (Mapsforge), see this issue: https://github.com/graphhopper/graphhopper/issues/1940

But offline routing should still work on Android. But as you need JDK 1.8 support this will exclude a few older Android versions and devices, I think.

Graphhopper. It has an Android client that uses its web service. You can also try out the web app.

This is now fixed and deployed. See the route here and the specific fixed examples here. Note that you can still find the dangerous spots via clicking the "stop" icon below the route information multiple times. But this is likely a result of the bad cycling infrastruture as cycle.travel contains these short dangerous parts too and if you do such longer routes for Germany it does not happen.

I'd suggest refactoring to use a self hosted version of Graphhopper (https://www.graphhopper.com/open-source/ - they have a docker image you can use and pass in an OSM file to build a graph on) or OpenRouteService to limit your cost exposure to google.

Open Source. The routing server is open source too and geocoding too.

Valhalla is great (I've contributed a few patches and run it for a while)!

Also check:

http://project-osrm.org/

https://www.graphhopper.com/open-source/

if you attached a geolocation to each meeting that should be possible. either using the google maps API or a self-hosted graphHopper instance

I just improved the documentation for the map matching a bit. Maybe this also helps a bit.

Well, JTS Topology Suite was first written in Java and then ported to other libraries: https://github.com/locationtech/jts#derivatives-ports-to-other-languages