Cloudscape : Open- sourced UI by AWS
Cloudscape is an open source design system to create web applications. It was built for and is used by Amazon Web Services (AWS) products and services. They created it in 2016 to improve the user experience across web applications owned by AWS services, and also to help teams implement those applications faster. Since then, They have continued enhancing the system based on customer feedback and research.
Source and details: https://cloudscape.design/