ZITADEL is an open-source identity and user management tool, and an alternative to Keycloak. It’s lightweight (written in Golang), has flexible deployment options and is easy to configure and manage. It’s also multi-tenant, offers comprehensive features for building secure and scalable authentication systems, particularly for B2B applications, and has built-in security features like multi-factor authentication and audit trails. By using ZITADEL, developers can reduce development time, enhance application security and achieve scalability for growing user bases. If you're looking for a user-friendly, secure and open-source tool for user management, ZITADEL is a strong contender.