A Visual Studio 'Shared Project' allows code and assets to be shared amongst other projects.
Shared Project is a new project type that first appears in Visual Studio 2013 Update 2. The code (and assets) in a shared project are included in other projects at compile time.
This may be used as an alternative to Portable Class Libraries, such as when sharing code amongst projects which in their entirety are not cross-compatible.
For example, a solution which has multiple projects that build separate executables for alternative platforms (such as Android and iOS). The Shared Project may hold common code and assets that work on both platforms.