ory/kratos: Headless cloud-native authentication and identity management written in Go. Scales to a billion+ users. Replace Homegrown, Auth0, Okta, Firebase with better UX and DX. Passkeys, Social Sig

Ory Kratos is an open-source, API-first identity and user management system written in Go that handles authentication flows like login, registration, account recovery, and multi-factor authentication. It offers deployment options through the managed Ory Network or self-hosted installations with optional enterprise licensing for production workloads. The system integrates with other Ory components (Hydra for OAuth2/OIDC, Oathkeeper for access proxy, Keto for permissions) and is used by major companies including OpenAI, Fandom, Cisco, and Klarna to manage billions of users.