"Subscriptions" is merely the list of the calendars one may select and download, aka subscribe (free). It is for the Mac and Apple is the subscription site, here.
There are hundreds of choices: holidays of (most) all religions and countries, activities/play dates of sports teams & entertainers, celestial calendars, historical dates, etc.
I read somewhere that Apple hasn't updated the list to which you linked since the advent of the App Store, and a quick look at it seems confirmatory.
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In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
