[martindevans]

There used to be .NET Framework (which was a Windows only runtime built by Microsoft) and Mono (an open source implementation for various other platforms).

In 2016 they started building .NET Core which is new open source implementation (built mostly by Microsoft) which runs on more platforms. For a while all three existed side by side.

Eventually .NET Core caught up and overtook the other implementations. These days Framework is legacy. Core has been renamed to just .NET (since it's now _the_ runtime) and Mono (as far as I know) has been totally replaced by it.

This is all from memory, so apologies for any inaccuracies!

[oaiey]

While correct, modern .NET supports currently two VM: CoreCLR and MonoVM. The later mainly as AOT compilation target for iOS, Android and WebAssembly. Mono is still better suited for that, but the AOT compilation of CoreCLR is progressing.

I think there is nothing else left from the Mono project like the class library or the compiler/toolchain.

[pjmlp]

Actually, .NET Framework is the Python 2 of the .NET world, with all the references that it entails.

Still too many enterprise products stuck in the old ways.

[Semaphor]

Unlike with python, some things simply can't be ported, though. I maintain a webforms page, the only upgrade path would be a full rewrite