Ant Design System for Figma - A large library of 2100+ handcrafted UI components
Google Open Source - All of Googles open source projects under a single umbrella
UI Playbook - The documented collection of UI components
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
DaisyUI - Free UI components plugin for Tailwind CSS
Open Source @IFTTT - A collection of IFTTT OSS projects.