Jack Dorsey, co-founder of Twitter, is in an app-building spy. After releasing Bluetooth-based message app called Bitchat Earlier this month, this weekend Dorsey revealed another application called Sun Day, which is apparently helping users track UV exhibition and vitamin D consumption.
The new program is Available by Testflight at iOSand its code is on GitHub for anyone clone.
Like other developers, Dorsey rides the Vibe encoding bandwagon. But instead of using cursor, claude code, or windsurf, he says He uses an open source coding tool called goose.
A sunny day is simply usable. It shows you the UV rate for your location along with details such as cloud cover, sunrise and sunset. You can choose your skin type from six options, and what kind of clothing you wear. Based on these parameters, the app will calculate how long you can expose your skin to sunlight before it fires.
The app also shows your minimum vitamin D. Start a session by hitting the “Track UV Exhibition” button, and after the session is over, the app will show how much Vitamin D you won during the session and on the day.
