Think of it as a combination of Bitmoji, Habbo Hotel, and Second Life. You can follow friends, meet new people, and do creative things like take photos together and customize your avatar. There's also an in-app currency that can be bought with real money or through exploration and "daily quests."
One of the games in the app, which is similar to Flappy Bird, is very popular.
But the app's popularity is mainly due to its heavy visual elements. "I got Zepeto because I saw all my friends memeing with it on social media. Decided, 'Hey, why not just see what that app is,'" says @moonlytn, a user who, like so many others, changed their Twitter profile pic to their Zepeto avatar.