The MTA's own SubwayTime app provides real-time train times based on the train's current locations. (This is new in the last year.) It even works when trains are running on different lines, changing which stations they stop at, etc.<p>I'm struggling to imagine what "live alerts from other riders" can provide on top of that?<p>Even for things like if a subway station is particularly crowded, or a train is particularly crowded... seems like that could be inferred from the train locations and average activity per-station for that day of the week.