This is a free service that will send your phone alerts on the arrival and departure status of trains in the USA.
It's useful—and provides value over the meager alerting offerings from the train operators—because it lets you set custom alerts for arbitrary trains at arbitrary stations. For example, if I know that I am going to pick up a train in Philadelphia that originates in New York, I can set an alert for the departure of the train from New York. If the train departed late from New York, chances are it will arrive at least as late to Philadelphia. If my alert fires and the train still hasn't left New York, I can safely predict that the train won't arrive in Philadelphia for at least another hour.