Back in August, Google released the preview version of its Google Fit software development kit (SDK). Now the SDK has gone into general release -- which means we should see a glut of Google Fit-enabled apps shortly.
The preview version didn't allow apps to be published to the Play Store, so the general release is quite a big deal -- though online chatter suggests there are still some teething problems with the platform. Hit the announcement post for more details and the download links.
Google Fit SDK Available Now [Google Developers Blog]