The Metrological SDK contains several plugins and helpers that allow you to build TV apps and deploy them on the Metrological Platform.
The plugins in the Metrological SDK were previously an integral part of the Lightning-SDK. Since version 5.0.0 of the Lightning-SDK they have been moved (forked) to their own repository and are fully maintained by the Metrological team, instead of the Lightning Open Source team.
For now, the Lightning-SDK still exports the Metrological and platform specific plugins from this repository. So from a developer perspective nothing changes while developing a Lightning App using the Lightning-SDK.
Check out the complete SDK documentation for more info on each available plugin.
Check out the changelog here.