FreeBSD is quietly prevalent in commercial and government settings. Juniper and NetApp are just two renowned examples. There have been and are many others.

Separate from any of those, a good chunk of America's more sensitive production database clusters, other workloads, and some network applications are scheduled by Nomad or Kubernetes running directly on a kernel that is not Linux.

The most popular kernel is not necessarily appropriate for all use cases or types of environments where high-value targets reside.

Directly downstream of FreeBSD, HardenedBSD achieved its long history of invulnerability to what were exploitable vulnerabilities in upstream through its advancements in the operating system layer.

  https://hardenedbsd.org/content/easy-feature-comparison

> but security thru obscurity

Arrogance is stupidity.