1. Integrating with mobile sensors.
2. Human activity detection app.
3. Pedometer app development.
4. GPS, Geolocation app development.
5. User positioning and beacon app development.
I have used several sensors such as Mbientlab made IMU fusion sensors and China made cheap sensors.
Also perfectly integrated with mobile apps and get full data from the sensor for detect human activity.
This will be good point for you who is going to start to work with fitness or health application.
Thanks