Board Game Arena

Can anyone tell me what it means when you have a green check with a star beside it? I know the checkmark means it's free but what does the star indicate?

The star means it’s free because of another card (chaining) or wonder stage (Olympia).

It also shows you the number, what it would have cost if you didn't have the chaining or wonder effect that makes it free. Useful when your wonder makes the first card of each round free, so you can see what this card will cost you if you don't play it now and it comes back around before the round ends.