The Microsoft .NET Framework 4.5 is a highly compatible, in-place update to the .NET Framework 4. By using the .NET Framework 4.5 together with the C# or Visual Basic programming languages, you can write Windows Metro style apps. The .NET Framework 4.5 includes significant language and framework enhancements for C# and Visual Basic so that you can more easily write asynchronous code, the blending of control flow in synchronous code, a responsive UI, and web app scalability. The .NET Framework 4.5 adds substantial improvements to other functional areas such as ASP.NET, Managed Extensibility Framework, Windows Communication Foundation, Windows Workflow Foundation, and Windows Identity Foundation. The .NET Framework 4.5 delivers better performance, reliability, and security.
Software that can be used as an alternative to Microsoft .NET Framework: