Somewhat confusingly, the name has been changed from what would have been ASP.NET 5 to ASP.NET Core 1.0, while Entity Framework 7 (when it appears) will now be called Entity Framework Core 1.0.
.NET Core is, of course, the open source version of .NET that was introduced in 2014, see .NET Core The Details - Is It Enough?. It too is to have its numbering changed with the upcoming version designated .NET Core 1.0
The thinking behind the renaming is that ASP.NET is something that developers understand and use, but the next version is newly written from scratch and isn't actually a replacement. ASP.NET 4.6 remains supported and released, and is more complete than the .NET Core version.
The need for redeveloping the .NET platform is to enable it to become cross-platform and open source, and to have a modular design. This opens the way for features such as native code compilation so that performance can be improved.
The full renaming is:
ASP.NET 5 is now ASP.NET Core 1.0
.NET Core 5 is now .NET Core 1.0.
Entity Framework 7 is now Entity Framework Core 1.0
Writing about the new version, developer evangelist Scott Hanselman says:
"The whole .NET Core concept is new. The .NET CLI is very new. Not only that, but .NET Core isn't as complete as the full .NET Framework 4.6. We're still exploring server-side graphics libraries. We're still exploring gaps between ASP.NET 4.6 and ASP.NET Core 1.0."
ASP.NET Core 1.0 is a 1.0 release that includes Web API and MVC but doesn't yet have SignalR or Web Pages, nor does it have support (yet) for VB or F#. These are planned for addition in the future. If you need these elements, ASP.NET 4.6 is still the option to go for.