InfoWorld recently published information about Microsoft's CBL-Mariner (which is where I first heard of this distribution). As InfoWorld noted, even though CBL-Mariner is a public release, it's meant for Microsoft's own use. It's a lightweight Linux distribution that could be part of Microsoft's evolving 5G/edge networking plans in its Azure for Operators unit, as InfoWorld notes. Infoworld adds that in the past, Red Hat's CoreOS used to be the preferred host for Linux containers, but it's recently been deprecated, so users need an alternative. By creating its own distribution for its cloud services, Microsoft can update and manage the host and container instances on its own schedule, InfoWorld adds.
Microsoft made its initial CBL-Mariner commit on GitHub four months ago. It's available under an MIT License.
I've asked Microsoft for a list of its own products and services currently using CBL-Mariner and if and how it expects Microsoft customers and partners to use CBL-Mariner. No word back so far.
Update: A spokesperson said Microsoft had nothing more to share on this topic. (Me: Hmmm.)