The OpenStreetMap-api-client PHP SDK by Mauro Moreno is a PHP client for the OpenStreetMap API. The OpenStreetMap API has various aspects. Part of it's services provides read and write operations on the raw map data of the OpenStreetMap database.
Online mapping pioneer MapQuest is using open data to provide transit directions via its MapQuest Directions API and the OpenStreetMap-based MapQuest Open Directions API. In both cases, transit directions are based on the Google-created GTFS data standard that helps transit agencies share their routes, schedules and fares in a consistent format. Currently MapQuest's support is limited to six U.S. metro areas.