authentik is described as 'open-source identity provider focused on flexibility and versatility'. There are more than 10 alternatives to authentik for a variety of platforms, including Online / Web-based, Self-Hosted solutions, Windows, Linux and Mac. The best alternative is Keycloak, which is both free and Open Source. Other great apps like authentik are FreeIPA (Free, Open Source), FusionAuth (Paid), LoginRadius (Paid) and Okta (Freemium).
FreeIPA is an integrated security information management solution combining Linux (Fedora), 389 Directory Server, MIT Kerberos, NTP, DNS, Dogtag (Certificate System). It consists of a web interface and command-line administration tools.
FusionAuth is auth for any app. Get everything you need for secure registration and user management in minutes. Single-tenant, on-prem or private cloud, custom emails with localization, social login, and more.
10Duke Identity Provider makes it easy for your customers to access and register to multiple applications with single username and password or using their favorite social login, secures profile data and easily integrates with leading business tools.
LemonlLDAP::NG is a modular Web-SSO based on Apache::Session modules. It simplifies the build of a protected area with a few changes in the application. It manages both authentication and authorization and provides headers for accounting.
Ory builds cloud-native authentication (login), authorization (permission), delegation (OAuth2, OpenID Connect), and user management software. You can deploy what you need yourself or use the Ory Cloud Platform and get started in minutes.