Kai Koerber was a junior at Marjory Stoneman Douglas High School when a gunman murdered 14 students and three staff members on Valentine’s Day in 2018. Seeing his peers — and himself — struggle with returning to normal, he says he wanted to do something to help people manage their emotions, on their own terms. The result was Joy, an app built on AI that helps people struggling with sadness, grief or anger to find help in short, bite-sized prompts and tools.