This app was mentioned in 2 comments, with an average of 8.50 upvotes
Trimet mobile app:
https://play.google.com/store/apps/details?id=org.trimet.mt.mobiletickets
Trimet transit tracker
https://play.google.com/store/apps/details?id=com.beagleapps.android.trimettrackerfree
Ingress
https://play.google.com/store/apps/details?id=com.nianticproject.ingress
Yes there is an app
Android link
IOS link