This app was mentioned in 2 comments, with an average of 4.00 upvotes
For local routes there is: http://boulderbustracker.com/
The mobile-web version is not great. There seems to be two different Android app versions available. I don't know which is better.
https://play.google.com/store/apps/details?id=com.etatransit&hl=en
https://play.google.com/store/apps/details?id=com.cherish.BusTracker
EDIT: After a quick comparison, I think ETA Spot is the better app. Main advantage is you can view multiple routes on the map at the same time.