Microsoft has made the Windows Server Core base image available on MCR, and that's a version of Windows Server 2019 which has much of the functionality of the full server edition, but without the UI. As base images go, it's very large: 2 GB compressed on Docker Hub, compared to 100 MB for Nano Server, and 2 MB for the tiny Alpine Linux image. But it means you can Dockerize pretty much any existing Windows app, and that's a great way to start migrating your systems to Docker.
Remember NerdDinner? It was an open source ASP.NET MVC showcase app, originally written by Scott Hanselman and Scott Guthrie among others at Microsoft. You can still get the code at CodePlex, but there hasn't been a change made since 2013, so it's an ideal candidate for proving that old .NET Framework apps can be migrated to...