Jack Dorsey, a co-founder of Twitter, is developing a lot of apps. Earlier this month, Dorsey released Bitchat, a Bluetooth-based texting app, and called it an open source chat app in which the Bitchat app and software Lacks Security Review. This weekend, he created and unveiled a new app that measures your vitamin D levels and sun exposure, Sun Day, another software that supposedly tracks vitamin D intake and UV exposure.
The code for the new app is available on GitHub for anyone to clone, and it is available on iOS through TestFlight. The app shows your local UV index and hours of sunshine based on location-based data. The app will track your approximate vitamin D levels for the day, how long you can be in the sunshine without burning, and your skin type and clothing level. You can also manually toggle when you’re in and out of the sun.
Dorsey is following the trend of vibe-coding, just like other coders. However, he claims that his latest weekend coding projects, which he is using Goose, an open source coding tool, are helping him “learn” in place of Cursor, Claude Code, or Windsurf.
Just last week, a $3 billion agreement for OpenAI to acquire AI coding tool Windsurf fell through, as Google jumped in to lure Windsurf’s CEO and top talent onto its DeepMind team. It and similar feel coding tools are among the next major battlegrounds for tech’s AI titans.
Using Sun Day is easy. Along with information about cloud cover and dawn and sunset times, it displays the UV Index for your current location. Six skin types are available for you to select from, along with the sort of apparel you’re wearing. The app will determine how long you can expose your skin to sunlight before it begins to burn based on these characteristics.
Additionally, the app displays your minimum intake of vitamin D. When you tap the “Track UV exposure” button to begin a session, the app will display the amount of vitamin D you have acquired throughout the session and throughout the day.