What is a sound decentralized app that was curated by IcoDrops where the app depended on blockchain-based tokens and could potentially scale up to millions of u

What is a sound decentralized app that was curated by IcoDrops where the app depended on blockchain-based tokens and could potentially scale up to millions of users based on that same blockchain? Or that isn't possible, what's a decentralized app that is still valuable technology which doesn't need to scale up like that?