In June I blogged about the SharePoint Framework Extensions Developer Preview and last night the SharePoint Framework Extensions moved a step forward, they are now available as Release Candidate 0:
https://dev.office.com/blogs/sharepoint-framework-extensions-rc0-now-available
Not completely ready so to say, my guess there will be at least two more RCs but at least they moved out of Preview.
If you don’t know what the SharePoint Framework Extensions are, just jump back to my June post to read all about it.
Have Fun!