Microsoft .net Framework 4 Multi Targeting Pack -

The .NET Framework 4 Multi-Targeting Pack is a set of libraries and tools that enables developers to create applications that can run on multiple versions of the .NET Framework, including .NET Framework 4, .NET Framework 3.5, .NET Framework 3.0, and .NET Framework 2.0. This pack is designed to simplify the development process and reduce the complexity of targeting multiple .NET Framework versions.