I have used this app for a couple of years. It works OK with one glaring exception.
It sorts the inbound and outbound trains by departure time from the outermost stop. The problem is, 5 trains per day on my line (FITCHBURG) do not originate at the outermost stop. The algorithm used by this app puts all of these trains at the end of the day. As a result the "next train" function as well as the schedule displayed within the app are inaccurate.
Sounds like not a big deal but I have alerted the developers twice about this bug over the past year+ with no result. I wouldnt bother with this app since the developer has no interest in making it function correctly.
Commuter_user about OpenMBTA, v1.4.1