VSCUnity
Unity3D editor plugin to make Unity projects Visual Studio Code compatible.
Add to /Assets/Editor/VCSUnity and then choose "Update project for Visual Studio Code" from the "VS Code" menu.
Currently just searchs the project folder for .sln files and replaces the VS2008 header with the VS2012 one, then appends .hide to the -csharp solution's extension so that Visual Studio Code knows which one to open. MonoDevelop/Unity doesn't seem to care about either change but this is a quick hack so I won't be held responsible for loss of life or limb. ;)
Prompted from @prime_31's note that Xamerin projects open correctly in Visual Studio Code.