Comment by freeone3000

Entra (prev AAD) can be replaced by literally any other OAuth provider for SSO - shibboleth is an on-prem option.

Traditional AD is harder to replace, but OpenShift’s IdP has an AD server mode that is capable of many use-cases; the cases it doesn’t do are GPO, Windows Update forcing, and other stuff no longer relevant on linux.

Are they moving away from Exchange Server? I’d hope so, MTAs are a dime a dozen in linux land. There’s a dozen homegrown alternatives for calendar + mail, from ProtonMail to running Exim + caldav.

The rentier companies may have “extended” the open source backing, but you’re not missing much except marketing.