Donations, actually. It still operates at a net loss, but the costs are offset.
But to make it a bit more relevant, where would you put Canonical on this list? Ubuntu is given away for free, they don't sell their users (with the very arguable exception of the Amazon lens fiasco), yet they make their money by selling professional services (Landscape and the like).
I would still place that as a community project (or community service project), which is used as a loss leader for their commercial (support) offering. And, according to recent controversy surrounding their desktop search, some would argue that they are moving to their users being the product.
But to make it a bit more relevant, where would you put Canonical on this list? Ubuntu is given away for free, they don't sell their users (with the very arguable exception of the Amazon lens fiasco), yet they make their money by selling professional services (Landscape and the like).