An app-based game where the player has to reach out to strangers around them and get them to do stuff. The tasks are designed so that the participants are likely to have fun/rewarding experiences after they overcome the awkwardness of the situation. The tasks get progressively more funny, awkward, and challenging - especially to people that are not comfortable talking to strangers.
The game can be played in multiplayer mode. This basically means that a group of friends see each other's finished/unfinished tasks. They would naturally be inclined to tell each other how it went. They can do so in the group chat. This adds a layer of accountability to the game.
Help people socialize in person rather than via the internet
Create interesting stories that people will remember
Instill a habit of talking to people
Help introvers make new friends
Help people realize that a lot can be achieved by just taking the first step
The tasks would start out easy. There would be a few to warm up sessions every day to get the player "in the zone". Stuff like "show a stranger a photo of your pet and get their opinion on it". Soon enough, the tasks would get more challenging like "get one stranger to record a video of you trying to perform this dance on the street while their friend has to play the role of the background helper guy in the video and cheer you on".