General Transit Feed Specification is a format for public transit agencies to publish this information. There are a few repositories like https://transitfeeds.com.
This looks really cool! I gotta figure out a way to contribute to this. Is this what OsmAnd uses to pull in transit information?
OsmAnd has directions in beta (using GTFS and OSM route markings) but it's pretty bad at the moment!
What's the best way to help? Do I just add the feeds to another website somewhere?