Most transit APIs use GTFS (General Transit Feed Specification), or if you want real time info, GTFS-rt (rt for realtime).
GTFS should come in a ZIP, and when unzipped, contain .txt files (which are actually csv files!)
Parse using whatever your language uses for csv parsing from there, and extract data!

GTFS-rt is harder to parse as it uses .proto and works differently! Some libraries may help, but I recommend looking at docs (especially Google's docs) for help!
You will also certainly find this useful, as it contains many libraries for GTFS parsing!
Finally, I highly recommend you read this blog post, it is extremely helpful and walks you through more about what GTFS is, contains, and where the data can be found!
psst, you may also want to check if your local transit system runs a developer API :3c

Yea! It's called KnoWMATA (because it's WMATA), and it is a very simple website demonstrating a few features (check the backend!)
Find the game here and the repository here!

Good question! As long as its accessible on mobile, gamifies transit, and uses real data and can be played in real life, you are free to submit it! (and if you can find a way to involve planes, then that's super silly and you can totally submit it :D)
it's highly recommended to do an app that utilizes your local transit system (for ease of demonstrating that it works), but if not, it is 100% okay to have data from another system (and have your app work in that system!)

Some examples are the line indicators right on this website (stickers)! There'll also be stuff like a RFID card themed like a DRHC (Democratic Republoc of Hack Club) Card, and other stickers too! Another option are grants for you to use in your local transit system!

You can also choose to have us buy merch for you! (rate is 5$/hour tentatively as thats the general guideline)

Join #hackroute and RSVP!

Public transit + planes! If you have another form of transit in mind dm @niko on slack to see if you can use it!