Currently available on iOS via TestFlight, Sun Day is an open-source app hosted on GitHub, reflecting Jack Dorsey’s hands-on approach to wellness tech using Goose instead of mainstream AI coding tools
Twitter co-founder Jack Dorsey has unveiled a new wellness-focused app called Sun Day, designed to help users monitor their UV exposure and daily vitamin D intake. The app comes just weeks after he introduced Bitchat, a Bluetooth-based messaging tool.
Currently available through Apple’s TestFlight program for iOS users, Sun Day is an open-source project, with its code publicly accessible on GitHub. The app reflects Dorsey’s growing interest in personal health tools and his hands-on approach to development, reportedly using the open-source coding tool Goose rather than mainstream AI coding assistants.
Sun Day offers a clean, minimalist interface displaying the UV Index for a user’s current location along with supporting environmental data such as cloud cover, sunrise, and sunset times. Users can input personal information including skin type—selecting from six predefined categories—and clothing coverage to estimate safe sun exposure time before potential skin damage.
The app also includes a feature to calculate vitamin D absorption. By starting a timed session through the “Track UV exposure” button, users can monitor their exposure and receive feedback on estimated vitamin D levels gained during that period.
The app aligns with a broader trend of developers creating lightweight, lifestyle-focused applications, often with open-source transparency. With Sun Day, Dorsey adds a health-conscious tool to his growing portfolio of experimental software, positioning it as a practical resource for those mindful of their sun habits and nutritional well-being.
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