The first business unit I was assigned to at IBM was Analytics Platform. The unit was responsible for twelve different web experiences. When I joined the unit, there was already a formal style guide in place. However, there was no reusable code for the twelve product teams to use. I lead the charge in getting distributable vanilla JavaScript and React component libraries created.
The projects taught me a lot about developer experience and accessibility. It was also my introduction into the design system industry. Since then, IBM has standardized to one component library: Carbon. It has been cool to watch the Carbon Design System actually inherit components and former team members.