There is any geocoding/routing service which runs on Google App Engine? (besides the Google Maps API)
App Engine doesn't have built-in geocoding or routing, so you're left with two options: Load map data into App Engine and geocode/route locally, or call out to a web service.
The former isn't a particularly good use of App Engine (or particularly practical). The latter works just fine - but means that the selection of GIS services available is exactly the same for App Engine as it is for every other platform. You mention one yourself - the Google Maps API.