Nuvem Consulting published its opinion about the five most useful IoT applications.
. According to this article they are:
1. Glowcaps: The medication taking reminder.
2. bikn: Help us to find our stuff (keys, phones)...
3. ParkSight 2.0: Help us find parking.
4. Sightmahine: Help in monitoring manufacturing processes.
5. Airqualityegg: Monitoring air pollution
Note that the first three is in the consumer space, one in the industry space, and one in the public/ sustainability space.
I guess that the "top 5" is subjective, but all of them are good examples of useful solutions in the IoT space.