Stack Auth is an open-source authentication and user management platform designed for developers. It offers features like password management, SSO, 2FA, and a headless SDK for integration. Stack Auth differentiates itself by being fully open-source, self-hostable, and significantly cheaper than competitors like Auth0. The platform is built for developers, allowing them to own their authentication processes while providing a responsive design and easy integration with Next.js and Postgres. With a growing user base and positive feedback from early adopters, Stack Auth is positioned as a reliable alternative in the authentication space.