whatsthe.app is a website that publishes verified revenue numbers of consumer (B2C) mobile apps on a public leaderboard, and runs a marketplace where founders buy and sell such apps. MRR, monthly recurring revenue, is the subscription income an app earns each month.
An app owner connects the app with a read-only API key from a revenue source: RevenueCat, Adapty, Superwall, App Store Connect, Google Play or Stripe. The site pulls revenue, MRR and ARR from that source, so the numbers do not depend on a seller's screenshots. RevenueCat and Adapty data update once per hour, store data once per day. The site states that it reads no user data, and an owner can show the revenue of a "stealth" app while keeping its name hidden. Listings for sale show the asking price, MRR and the price multiple; offers, letters of intent, purchase agreements and escrow run on the platform.
Adding apps and viewing the leaderboard is free. Sales through the marketplace carry a platform fee, usually paid by the seller.