Crowdsourced navigation apps like Waze are helpful for avoiding the real-world hazards that conventional apps don't mention. But what if you use mass transit -- why can't you get alerts that go beyond official route closures and delays? You can now, if you live in New York City. Google incubator Area 120 has released an invitation-only Pigeon app for iOS that offers NYC subway directions based both on real-time train positions and user-submitted feedback. If a train faces an extended delay or there's a glut of people at a given station, you can switch lines and stops to make your commute a little faster (or at least, less painful).
There's no Android version, and it's not certain if or when Pigeon will support other cities. If the app takes off, though, it's easy to imagine this being useful in any city with a reasonably large public transportation system. Apps like Transit can tell you how to get from A to B using real arrival times, but they can't tell you what to expect during the journey.