The GraphHopper Directions API is a collection of routing related APIs: like the Routing API, the Matrix API, the Route Optimization API and the Geocoding API. See here for a more detailed comparison.

For example: the Route Optimization API is an efficient way to consume jsprit: properly configured for a lot of use cases, with a proper distance/time matrix calculated from the routing engine under the hood, with a simple JSON API and some advanced featured not in jsprit.