Real-time tracking of commuter-rail service

This makes a big difference especially when the system has a lot of delays. Commuters and other riders can check for themselves instead of waiting to hear from the T about delays, which let's riders make choices about alternative routes to their destination.

This will be super helpful in tandem with http://www.people.fas.harvard.edu/~wuensch/T/live-train-map-beta.html

Not sure why you felt the need to highlight one particular web-only app adam- there are a bunch of apps that have been delivering real-time MBTA data for years now.

I guess the interface is interesting if you want to browse the commuter rail system as a 'data tourist' - although most typical users are going to be interested in only one line at a time. And this UI isn't particularly well scaled for handheld use either.

Several good everyday-use options have already been mentioned. The one I use most often - OpenMBTA - was first devloped for the Open Government Hack Day in 2009. As a dev'er I like the fact that it's free, is made by Bostonians for Bostonians, is updated regularly, doesn't track or throw advertising at users (which is easy to confirm because it's open source), and is available on iOS, Android and mobile web platforms.