It's was proof of concept showing how managed (.NET, CLR) exceptions could be thrown from X++ code in Microsoft Dynamics 365 for Finance and Operations. It's not needed anymore, because D365FO now has such a feature.
Refer to the blog post Throwing managed exceptions from X++ in D365FO for more details.
To run the code, you must put the content of the Metadata folder to the modelstore of D365FO (e.g. C:\AOSService\PackagesLocalDirectory or K:\AOSService\PackagesLocalDirectory).Then you can build the Visual Studio solution and run the code. Sample code is in the project called Example.
Code was built on platform update 20.