Jack Dorsey launches new app “Sun Day”

Twitter co-founder Jack Dorsey has introduced a new wellness-focused app called Sun Day, designed to help users monitor sun exposure and track their vitamin D intake.

The launch of Sun Day follows his earlier release of Bitchat, a communication app that works without internet connectivity.

Sun Day uses real-time data from a user’s phone location to calculate the UV index in their area. It then allows users to log their time in the sun manually, factoring in variables like skin type, clothing, and weather conditions to estimate vitamin D synthesis.

The app also provides insights such as sunrise and sunset times, cloud cover, and a personalized “burn limit” based on the current UV index — helping users stay safe while getting adequate sunlight.