Use Content Staging to push content from a private staging instance to your production site.
Use Content Syndication to automatically share content between any number of sites, in any direction.
Use Content Pools to push content from one site and allow editors to pull it manually into another site.
Content Sync is extremely flexible, so you can combine any of these use-cases with manual / automated push + manual / automated pull behavior, update behavior, different reference handling and a lot more.