Jack Dorsey Launches Sun Day App to Track Vitamin D and Sun Exposure

Highlights

Twitter co-founder Jack Dorsey’s new app Sun Day tracks your sun time and vitamin D levels with open-source AI tools.

Twitter co-founder Jack Dorsey is back with another side project — this time, an app to help people track their vitamin D. After unveiling his encrypted messaging app Bitchat just last week, Dorsey has now launched Sun Day. This iOS app monitors sun exposure and vitamin D intake.

Currently available through TestFlight, Sun Day’s code is open-source on GitHub. The app utilises location data to display your local UV index and daylight hours. Users can log their skin type, clothing coverage, and toggle when they’re in or out of the sun. The app then estimates your vitamin D levels for the day and suggests how long you can stay in direct sunlight safely.

Dorsey says he’s “learning” through these weekend coding experiments, which he’s building using Goose, an open-source AI coding tool. Tools like Goose are shaping up to be a hot space for tech’s AI leaders — just last week, OpenAI’s $3 billion attempt to buy Windsurf, another AI coding platform, fell apart after Google hired its CEO and key talent for DeepMind instead.

The Twitter co-founder seems determined to keep “vibe coding” alive — one quirky weekend app at a time.