The Author Showcase post features posts that were upvoted by the @curie account in the past week. Anyone can receive a @curie upvote, so in that sense, the Author Showcase is open to all. You can read the @curie Whitepaper to learn more about Curie.
Cheers - Carl
really @carlgnash, post @ curie in some time is very amazing, @curie very generous in giving vote to beginner steemit