A partial directory of the many applications that consume and utilize GTFS data is maintained at TransitWiki.
Many types of applications consume GTFS data, including:
Trip planning and maps – applications that assist a in planning journeys from one location to another using public transportation and other modes
Timetable creation – to create a printed list of the agency’s schedule in a timetable format
Accessibility – applications that assist transit riders with disabilities in using public transportation
Planning & analysis – applications that assist transit professionals in assessing the current or planned transit network, including ridership forecasting
Real-time transit information – applications that use GTFS data along with a real-time information source to provide estimated arrival information to transit riders
Public Information Displays - electronic displays to show schedule information, service advisories, real-time arrivals and/or other information