<PackageReference Include="NETStandard.Library" Version="2.0.0-preview2-25401-01" />

System.AppContext

public static class AppContext
namespace System { public static class AppContext { public static string BaseDirectory { get; } public static string TargetFrameworkName { get; } public static object GetData(string name); public static void SetSwitch(string switchName, bool isEnabled); public static bool TryGetSwitch(string switchName, out bool isEnabled); } }