It's a common API for things like networking, IO, threading, serialization, and so forth. Library authors need to do refactoring to achieve compatibility acros

It's a common API for things like networking, IO, threading, serialization, and so forth. Library authors need to do refactoring to achieve compatibility across .Net Platform (old stuff, Windows-only) and .Net Core (new stuff, cross-platform). This is the bridge for library authors to transition from being Windows-only to cross-platform. Think about library authors that need to write for both Python 2 and Python 3, there needs to be a common API between both, and this is it: .Net Standard. Meanwhile .Net Core is cross-platform build tooling and a minimal API.