(See update at bottom)
SunTracker is an open source application developed by Living Streets Alliance in conjunction with Open Tucson. Using publicly available data streams, volunteers created a web service to allow anyone to access real-time bus arrival information. SunTracker is one of two applications created to demonstrate the utility of this service. SunTracker is a mobile application for smart phones that can detect your current location and present the nearest SunTran bus stops. The app is also able to scan QR codes to load up the correct station information. You can then choose one and see real-time bus arrival data. The other application is a kiosk-based app that operates in much the same way, but it intended for installation in fixed locations such as cafes or libraries that will display arrival times for nearby stops.
Both applications are intended to make bus riding more attractive for “choice” riders — people who don’t have to take the bus, but might if it was convenient enough. SunTracker gives potential riders more control over their schedules by removing some of the uncertainty surrounding public transportation schedules and encourages people to leave their cars at home. BE AWARE: this software is in BETA and is not endorsed or supported by SunTran. We are hoping to get their stamp of approval at some point, but for the time being if you have problems with the software, let us know — not them.
Update: As of mid-2016, the suntracker app is no longer available. SunTran changed their API and our implementation stopped working. Real time data is available through the suntran website; you can see live route data on google maps.
Update #2: April 2018
It looks like a commercial app has taken up the slack: