.NET Core is on Github

CoreCLR is the .NET execution engine in .NET Core, performing functions such as garbage collection and compilation to machine code. .NET Core is a modular implementation of .NET that can be used as the base stack for a wide variety of scenarios, today scaling from console utilities to web apps in the cloud.

For those of you who missed what .NET Core is all about, this is a must read:

http://blogs.msdn.com/b/dotnet/archive/2014/12/04/introducing-net-core.aspx