Here's a list of useful links that will help you learn all about open data and assist you in developing great apps:
Google Transit API - the official Google Transit API website, which provides specifications for exchanging both static and realtime public transit information, including information about stops, routes, schedule, service alerts, and other details.
Google GTFS Overview - the General Transit Feed Specification (GTFS) can be used to share static public transit data.
Google GTFS Realtime - the GTFS-realtime Specification is an extension to GTFS that can be used to share realtime public transit data.
Google GTFS Proto File - this file specifies the hierarchy of elements and their type definitions. Here is a link to the TfNSW Proto File which describes the tfnsw vehicle descriptor extension 1999 that includes aircond and wheelchair accessibility.
Data.gov.au - the federal government's data hub.
NSW Open Data Portal - the NSW government's data portal.
Stackexchange Open Data Community - get help and join in the discussion on Stackexchange's open data community website.
Transit Feeds - an extensive archive of public transit data for software developers, transit agencies and more. Browse and download official GTFS & GTFS-realtime feeds from around the world.
City of Sydney open data portal - datasets available to the public for general information, for the wider benefit of the community, and to encourage an accessible and connected city.