"Internal implementation package not meant for direct consumption.  Please do not reference directly. Provides the fundamental primitives, classes and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and exceptions. This packages represents the core package, and provides the minimal set of types required to build a managed application.Commonly Used Types:System.ObjectSystem.ExceptionSystem.Int16System.Int32System.Int64System.EnumSystem.StringSystem.CharSystem.BooleanSystem.SByteSystem.ByteSystem.DateTimeSystem.DateTimeOffsetSystem.SingleSystem.DoubleSystem.UInt16System.UInt32System.UInt64System.IDisposableSystem.Uri When using NuGet 3.x this package requires at least version 3.4."