Zitadel

ZITADEL is an open-source identity and access management platform built around a strict multi-tenant hierarchy - Identity System, Organizations, and Projects - with isolated data and policy scoping at each level. It provides single sign-on, multi-factor authentication, passkeys, OIDC, SAML, and SCIM out of the box, and every resource and action is available through gRPC, connectRPC, and REST/HTTP APIs.

Its architecture writes every mutation as an immutable event, giving a comprehensive, API-accessible audit trail rather than a set of selectively logged actions. ZITADEL Cloud and self-hosted ZITADEL run the same codebase, and the project is designed for zero-downtime updates and horizontal scalability without relying on external session stores.

ZITADEL fits teams building multi-tenant SaaS or B2B platforms that need native support for organizations and instance-level isolation, rather than bolting multi-tenancy onto a single-tenant identity system.