.NET core is one of the leading development platform
Microsoft had actually started shifting their paradigm in early 2014 towards becoming open. Scott Hanselman said in his blog Microsoft killed my Pappy in February 2014, where he mentioned about new Microsoft approach of Embrace, Extend, Hugs. Under this new paradigm Microsoft started shifted their libraries to Github.
Scott Hanselman – February 2014
Many groups are using Git with TFS internally for projects, we’ve open sourced (not just source-opened) huge parts of .NET and are still pushing.
A journey started to move towards new destination which was named .NET Core. Jamie Tailor explains in his blog post “A Journey in .NET Core” about all events, stand ups of Microsoft teams and detailed discussion videos of whole process.
On January 2016, Scott Hanselman announced death of .NET framework in his blog post ASP.NET IS DEAD, Introducing .NET Core. He explained idea of how ASP.NET is written from scratch to create a brand new framework and is it given name ASP.NET Core. It could be straightly called evolution of .NET to .NET Core. It was just announcement then as it was not done or released yet. Main idea of .NET Core was to fully revamped whole ASP.NET and start with something new, something advance, something which could meet with advance technology of era.
Microsoft then may be was in serious pressure after success of Node.JS, Python, ROR and many other open source projects which were extra ordinary fast, efficient and able to run cross platform. Programmers and Developers world wide were adopting these new technologies leaving Microsoft .NET Framework behind. It was hell required to step in new era of Open Source and open products for public to allow community contribution and also change the way how whole .NET works.
.NET Core was the result of all such effort and new platform was born with handful of libraries. At that time it only supported either console application or ASP.NET Core applications. Truly it was huge path ahead to go in this new technology era.