Windows

In general, it does. Unless you use .Net Core that allows you to run any application based on CLR ( another reference ) without need to have anything installed. Everything you need goes along with your application. Of course it has its limitations, but it can. You should soon have . Native Native available for all kinds of applications, today you can only run a few types.

But you can do a bundle with Mono and avoid this whole dependence. I just do not guarantee that everything will be the way you want, that everything you need will turn out. This form is very similar to what .Net Core offers.

Mono's own people do not usually recommend using Windows as much. Not that it has any problems, but. Net is better. There are cases where Mono may be the only option.

Linux / MacOS

The .Net Core is available here as well .Net Native must be available. Mono, of course, also works, but it tends to be legacy for most applications, but again, some applications will still make sense.

Extra information

It is possible to mix files assemblies generated with Mono and .Net, after all they must be compatible. Of course, nothing guarantees that your code will be compatible on all platforms. It's no use trying to run WPF on Linux, for example.

No need. Mono is Mono, .net and .net are two separate things. In fact proof is that you run Mono on Linux and Mac systems where there is no .net framework created by Microsoft. What may be creating your confusion and @bigown is that you can mix libraries created in .NET (Microsoft) with Mono libraries. But you can write your code completely in Mono and compile on Linux for example, if you re-compile it in .net it might possibly work 100%.

For more information read about ECMA and compatibility between .NET and Mono