FusionAuth and Auth0 are both customer identity management providers offering similar features such as authentication for web and mobile apps, unlimited users and groups, OAuth token and API key management, multi-factor authentication, private cloud deployments, full support for Authentication as a Service (AaaS), user search, and user management interfaces. However, FusionAuth stands out from Auth0 in terms of its free pricing model for unlimited users, true data isolation through single-tenant security, on-premises or air-gapped deployment options, customizable localization, configurable password encryption, and detailed reporting and analytics tools. Additionally, FusionAuth is a smaller company with more flexibility to accommodate unique customer needs, offering one-on-one support and customizations, whereas Auth0 is a larger corporation with more complex approval pipelines and corporate overhead.