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.
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.
GrowthBook is an opensource Feature Flagging and Experimentation platform.