Jack Dorsey, the co-founder of Twitter (now X), has been on a roll with launching his work. On Sunday, Dorsey took to X to reveal his new app Sun Day which is meant to track UV exposure and Vitamin D intake. This comes shortly after his previous app launch, Bitchat, earlier this month.
Sun Day claims to show the UV index for users’ location, as well as other details like cloud cover, sunrise, and sunset timings. Users can choose their skin type, and the kind of clothing they’re wearing, and the app calculates for how much time they can expose their skin to sunlight to avoid sunburn. It also provides users their minimum Vitamin D intake.
A session can be started by tapping on the “Track UV Exposure” button on the app. After the session ends, the app will show how much Vitamin D the user has gained throughout.
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Dorsey also mentioned he was using the open source AI-coding tool “Goose” for his “recent weekend coding projects.”
Goose, like Cursor, Windsurf, and ClaudeCode is a “vibe-coding” tool. Vibe coding refers to an approach to building software, where a person describes a coding problem to a Large Language Model (LLM), which generates the actual code. Vibe coding shifts the programmer’s role from manual coding to guiding, testing, and refining the AI-generated source code. Vibe coding seems to be the latest big thing — last week a $3 billion deal for OpenAI to buy AI coding tool Windsurf fell through, as Google swooped in to hire Windsurf’s CEO Varun Mohan and top talent for its DeepMind team.
Sun Day follows Dorsey’s release of the Bluetooth-based messaging app Bitchat. Bitchat is a messaging app that operates through Bluetooth mesh networks, allowing users to send messages without Wi-Fi or cell reception. While apps like this usually only work within a range of around 100 meters due to Bluetooth’s technical limitations, Dorsey said this app has an extended range, and can relay messages through peers to extend up to 300 meters, or 984 feet.
Dorsey referred to Bitchat as a personal experiment in “bluetooth mesh networks, relays and store and forward models, message encryption models, and a few other things.”
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Bitchat has received some scrutiny following Dorsey’s admission that the app and its code have not been tested for security measures, despite promising to deliver a “secure” and “private” messaging without a centralized infrastructure.
Dorsey has added a warning to Bitchat’s GitHub page: “This software has not received external security review and may contain vulnerabilities and does not necessarily meet its stated security goals. Do not use it for production use, and do not rely on its security whatsoever until it has been reviewed.”
Both Sun Day and Bitchat are currently available for Apple iOS users via Testflight.