FreeRadius - FreeRADIUS is responsible for authenticating one third of all users on the Internet.
PacketFence - PacketFence is a Free and Open Source network access control (NAC) system.
JumpCloud - Cloud-based directory services. Alternative to Microsoft Active Directory.
FusionAuth - FusionAuth is a CIAM platform that is 100% free for unlimited users.
Keycloak - Open Source Identity and Access Management for modern Applications and Services.
Foxpass - Foxpass manages users, groups, and SSH keys (plus a LDAP and RADIUS interfaces) to increase an organization's server and network security.