Stack is an open-source, self-hostable, highly customizable authentication and user management system.
We provide frontend and backend libraries for Next.js, React, and JavaScript. You can set it up in one minute and scale with the project as it grows.
Stack was built by repeat founders with strong technical backgrounds and is funded (among others) by Y Combinator and Guillermo Rauch. Check out our GitHub: https://github.com/stack-auth/stack