You can find C# examples in the HealthVault SDK. At this point, only developers who have signed agreements with Microsoft are allowed to deploy applications again live HealthVault data, but all developers can use our pre-production (PPE) environment for
It would help us answer if you could provide some more details about the application you want to write. What will it be able to do?
I'm not familiar with any device support for the fit bit, but data from it would likely come in using the Exercise data type. Pulse oximeters would use the Blood Oxygen Saturation data type.