Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Developers Get Access to Official Pebble Watchface SDK
Your patience has been rewarded…you have a brand new Pebble Smartwatch in your hands. And, of course, now you want to make it do your bidding.
This developer documentation will show you how to create your own functionality for a Pebble Smartwatch.
At this point in time the SDK is limited to creating different watch faces and does not support the creation of standard apps, though the Pebble website says that a Sports SDK will be added soon, allowing developers to incorporate Runkeeper-style features.
The new Watchface SDK comes alongside version 1.10 of PebbleOS, which also offers up options for disabling backlighting and vibrations along with several bug fixes for iOS users.