Microsoft’s Linux Group has been fairly public about its work on a Microsoft-created Linux distribution that is for the company’s internal use only. That variant, known as CBL (Common Base Linux) Mariner, is used across a variety of Microsoft products, from the Windows Subsystem for Linux GUI to AKS HCI, Azure Percept, and more. But it turns out there’s another Microsoft-developed Linux distribution that’s also for internal use that’s known as CBL-Delridge or CBL-D.