.NET Framework is still closed source AFAIK. .NET Core is open source, but that's two different things. Moving existing applications from .NET Framework to .NET

.NET Framework is still closed source AFAIK. .NET Core is open source, but that's two different things. Moving existing applications from .NET Framework to .NET Core and running them on Linux is still troublesome (for example lack of proper ODBC support on .NET Core). Serialization between the two is often not possible or not easy (differences in byte layout). While I think .NET Core is better than nothing, it all has a long way to go, including MS-provided API dlls (like ADOMD, etc.).