Twitter co-founder Jack Dorsey's new app, called Sun Day, ostensibly helps users track UV exposure and Vitamin D intake.

Jack Dorsey, co-founder of Twitter, has launched his second app within a week, Sun Day, designed to help users track their vitamin D intake.

The Sun Day app, just out in beta, will prompt you on how to prep for being out and about. The founder of Twitter, Jack Dorsey, has a bright idea that he's released as a beta app: Sun Day, for ...

Named Sun Day, the app tracks UV exposure and vitamin D intake for users at their location. It is currently available via ...