I'm sure that you heard about .NET Standard. To simplify the definition just one quote from the offical GitHub repo FAQ .NET Standard is a specification that represents a set of APIs that all .NET platforms have to implement. This unifies the .NET platforms and prevents future fragmentation. BTW in case you don't know just read the full article Introducing .NET Standard. On the other hand, Owin is (from owin.org): OWIN defines a standard interface between .NET web servers and web applications. The ...