GTFS Manager is the world's most used web application for maintaining GTFS data.

Transit Alerts publishes your service alerts in Google Maps using GTFS-realtime.

Show your riders the big picture in a zoomable map that updates with your GTFS.

Trillium builds rider-centric websites with responsive designs—for transit only.

visits soar to rome2rio, the international multimodal travel search site

rome2rio helps travelers to discover transportation between points on the globe, stitching together bus, train, ferry, air, and other options into multimodal itineraries. The site uses many sources for transportation data, including GTFS.

In Fall 2015, Travel Trends News reported that visits to rome2rio soared, bringing the site to profitability. I take this partially as a sign that travelers are looking beyond the obvious option of air-only itineraries with rental car and considering other modes.