This presentation by Melanie Edwards and Greg Whitworth is a great introduction to the Open UI project and its goals.
Today, component frameworks and design systems reinvent common web UI controls to give designers full control over their appearance and behavior. We hope to make it unnecessary to reinvent built-in UI controls, but for those who choose to do so, we expect that these design systems will benefit from Open UI's specifications and test suites.
Long term, we hope that Open UI will establish a standard process for developing high-quality UI controls suitable for addition to the web platform.open-ui.org
CSS Café is a monthly international meetup and has a great back catalog of previous sessions available to watch on YouTube.
Learn more about Open UI and get involved at open-ui.org