shadcn/ui
"Copy-paste" component library — Shad Cohen, 2023. You don't install an npm package; the CLI copies the component source code into your own repo.
Built on Radix UI (headless primitives for accessibility) + Tailwind CSS. The philosophy: own your UI code, modify freely, no "throw away the locale and upgrade" problems. Quickly became the default choice in Next.js/React startups.
Sweet spot: teams that want good default design and then control. Competitors: Material UI, Chakra UI, Mantine, daisyUI. shadcn/ui isn't a library — it's a distribution.