Far more clever apps turned out to be disappointments:
RainAlarm offered to warn us when it was going to rain, and show tv-news-ish weather maps to prove it. We turned out only to need that information once a day; it was easier to get elsewhere.
PointInside offered maps and GPS guidance inside large, confusing buildings, which means all of them within D.C., but was also extraneous. Even in a big crowd the problem indoors is far more often losing each other, not our way through the building.
MyCarLocator was a great idea, but also unnecessary in that case. There were so few parking options in D.C. it wasn't hard to remember where you parked. I'm leaving it installed, though, for mall parking lots, outdoor concerts and any other situation when there is lots of parking but no clear landmarks to help remember where it is.
Intercom looked cool, but wasn't useful. It lets users of Bluetooth-equipped phones talk via Bluetooth radio as they would with walkie talkies. Phoning or texting was easier.
GPS Essentials looked really cool. With waypoints, a compass, automatic camera, map, speed, location and altitude charts, a special map and visual guide to the GPS satellites to which you're connected, it's the all-in-one GPS travel app. We never needed such comprehensive information. All we wanted were real-time maps and text showing the next turnoff. Anything else was distracting.
Here I Am 2 looked like a great way to find each other when we were separated by letting us text or email our location to one another. Using it required contacting the other party first, which made it easier to solve where-are-you issues that way rather than by using the app.
What was unexpectedly great?