ASP.NET Core is a new open-source and cross-platform framework for building modern cloud-based web applications using .NET.
ASP.NET Core is completely open source, you can download it from GitHub (https://github.com/aspnet/Mvc). It's cross platform, which means that you can develop ASP.NET Core apps on Linux/macOS, and, of course, on Windows OS.
ASP.NET was first released almost 15 years back with the .NET framework. Since then, it's been adopted by millions of developers for large and small applications.
With .NET Core being cross platform, ASP.NET took a huge leap beyond the boundaries of the Windows OS environment for development and deployment of web applications. Let's look into more details of the cross-platform ASP.NET.