It's the Pro plan features that you see at https://leanpub.com/create/book (custom themes, Google Analytics, InDesign Export) for up to 100 books or courses.

Instead of paying $12.99/month (its current price), you can just make a one time purchase of one of the shelf spots which includes it at https://leanpub.com/shelf/buy ... the cheapest one which includes it is $349 (which is a Lifetime Pro Plan + a 1 month shelf spot), and there are $499 (which is a Lifetime Pro Plan + a 3 month shelf spot) and $699 (which is a Lifetime Pro Plan + a 6 month shelf spot) options also available.

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