Angel, is a super interesting wearable device coming up from indiegogo.
This project really looks awesome:
Angel is the first device designed with developers in mind. Currently most trackers for fitness and health are built for use by a single proprietary app. We want to change that. We are opening up every protocol, API and sensor data stream. Ultimately, this means more apps to choose from.
When it comes to openness, the Angel project dubs itself as open both in software and hardware.
That would be a great choice, as only an open hardware ecosystem (coupled with apps) could provide a good level of experimentation.