Storybook is a frontend workshop for building, documenting and testing user interface components and pages in isolation. Teams add it to a project through an npm package and, according to the website, use it for UI development, testing and documentation. The source code is on GitHub under the MIT licence.
Storybook is an open-source project. Chromatic, a commercial platform that calls itself the official Storybook platform and offers visual testing, review and hosting, states that it is made by the maintainers of Storybook. The company behind it, Chroma Software, Inc., uses California law in its terms and a San Francisco notice address, so the organisation sits in the US. Because Storybook itself runs locally, no data leaves your organisation unless you choose a hosted service such as Chromatic, whose data location is not stated. As the code is open, you can inspect and run Storybook on your own infrastructure without depending on a vendor.