Please see the react/fabric blog post here.
PowerApps component framework enables professional developers to create reusable, responsive and configurable custom UI components for model driven PowerApps (Dynamics 365) and we will be releasing support for canvas apps as preview soon. This will enable developers to build the control once and reuse across both platforms on different form factors. New unified interface for Dynamics 365 is build using this framework so you are already using it.
To learn more about the framework, please see the preview announcement blog post here.
You can see and try some cool sample controls built by community here.
If you have any questions or discussion topics, framework community forum link is present on the PowerApps community here.
Thanks,
Hemant