Microsoft has made .NET opensource and crossplatform, now what happens to alternatives that was provided before to offer .NET on other platforms. Oh one last thing, does this mean I use my c# code and compile it for linux now?
Felix the Microsoftie here. You've been able to use C# code and compile for Linux for a while now - thanks to Mono. The challenge is that the Windows implementation has one code base while Mono has a complete separate code base.
The Mono community was essentially forced to re-implement .NET because no open source implementation was available. Customers have reported various mismatches, which are hard to fix because neither side can look at the code of the other side. This also results in a lot of duplicated work in areas that aren’t actually platform specific. The best way to build a cross-platform stack is to build a single stack, in a collaborative manner. Mono and .NET aren't one, but they'll be able to work together in an unprecedented way. There's Linux stuff in Mono that we would like to use (and vice versa).
The Mono community was essentially forced to re-implement .NET because no open source implementation was available. Customers have reported various mismatches, which are hard to fix because neither side can look at the code of the other side. This also results in a lot of duplicated work in areas that aren’t actually platform specific. The best way to build a cross-platform stack is to build a single stack, in a collaborative manner. Mono and .NET aren't one, but they'll be able to work together in an unprecedented way. There's Linux stuff in Mono that we would like to use (and vice versa).
To answer your last question: Yup.