Open Location Codes are a way of encoding location into a form that is easier to use than latitude and longitude. Source for a website to demonstrate Open Location Codes. (https://github.com/google/open-location-code)
Material UI is an open-source React component library that implements Google's Material Design. It's comprehensive and can be used in production out of the box.
Prisma is an open-source database toolkit. It includes a JavaScript/TypeScript ORM for Node.js, migrations and a modern GUI to view and edit the data in your database. You can use Prisma in new projects or add it to an existing one.
This package exports a few of the CSS variables that we use in Facebook projects. This is not the full list we have internally but focused on making available the minimum set needed by our opensource projects.