Something most people don't know is that Gmail, the inbox everyone is using, offers in-app purchases on the App Store.
I was a bit surprised too, having never seen one myself, but discovered it to be the case when I started noticing Gmail in the Top Grossing chart several months ago.
Google making money isn't really a surprise, but how fast it's growing and where the money is coming from are very interesting.

In November, Google's iOS app earned $8.9M of net revenue, according to our estimates. Net means what Google gets to keep after Apple takes it fee, and we're only looking at Apple because Google doesn't use a standard in-app purchase on Google Play.
Our estimates show November was Gmail's highest month of revenue ever. October was its previous high, and August before that.
Gmail's revenue has been growing consistently since the in-app purchase rolled out in 2021 with only a single decline in September.
What's Gmail charging for? Space! 100MB is Gmail's best earner with 200MB and 2TBs below it.
I fully expect to see Gmail climbing up the Top Grossing chart going into 2024.
May’s top app charts were mostly stuck, but ChatGPT kept growing in downloads while TikTok kept leading revenue and Google One climbed into the top five.
Apple's WWDC 2026 app song named a tiny slice of the App Store, but the apps behind the lyrics are far bigger, older, and more successful than average.