What does Server Core App Compatibility (FOD) really do on Server 2019?

App Compatibility allows a limited set of mmc.exe (.msc extension) applications. If you run mmc.exe from the cmd prompt and click File->Add/Remove Snap-in, you can see the list of included management tools.

You can also run them by themselves from the cmd prompt. Such as cluadmin.msc for Cluster Administrator, or diskmgmt.msc for Disk Manager, and my favorite, devmgmt.msc for Device Manager to easily install drivers (no more pnputil).

You can also run some Control Panel applets, such as Networking ncpa.cpl to view and edit network adapters.

You don't get a Start Menu, so I don't believe you can pin applications.

I only wish Windows Hyper-V Server 2019 included Hyper-V tools...