Where is Kerberos used in practice?

It is the standard authentication protocol of Microsoft Windows as an integral part of Active Directory, it is available for macOS, FreeBSD, Unix and Linux, and applications such as SharePoint, SAP GUI and Microsoft Entra SSO build on it.

• Windows domains: since Windows 2000, Kerberos is the default authentication method. It gives single sign-on to services, servers, files and devices such as printers and scanners. (It is sometimes loosely called an authorisation technology; strictly it authenticates. Windows adds group information to the tickets, which services then use for their own authorisation decisions.)
• Other operating systems: MIT Kerberos and Heimdal implementations run on macOS, FreeBSD, Unix and Linux; Linux machines can join an AD realm and use it for logon, SSH and NFS.
• Applications: SharePoint and intranet web applications (via the browser's integrated Windows authentication, SPNEGO), SAP GUI single sign-on, databases, and seamless SSO from a domain PC into Microsoft Entra ID cloud services.

Kerberos and LDAP often appear together: the directory holds the accounts and groups, Kerberos proves who the user is, and an LDAP bind via SASL/GSSAPI can itself use a Kerberos ticket instead of a password.

Go deeper:

• Microsoft Learn: Kerberos authentication overview — how and where Windows uses Kerberos.
• RFC 4752: The Kerberos V5 (GSSAPI) SASL mechanism — how an LDAP bind uses a Kerberos ticket.