Not very many businesses, but there are quite a few biiig ones.

Here on HN I often read startup stories about services which, on one hand, “nobody” has heard about, and which, on the other hand, “quickly grew to a couple million users and started having scalability problems”, which then spawns some story about scalability tricks. Always leaves me astonished as to how the heck some another glorified todo list/cat picture thing can rake millions of users so fast, but here we are.

I suspect there are way more niches in which tens of millions of users live, which the rest of us can just be ignorant of. It’s only when you approach a billion users that you can be sure “everyone” at least has heard the name of the service/app.