The namespace contains a lot of types and some are complex to replace.

Milestone I

• AccessViolationException
• Action
• Action`1-8
• AggregateException
• AppDomainUnloadedException
• ApplicationException
• ApplicationId
• ArgumentException
• ArgumentNullException
• ArgumentOutOfRangeException
• ArithmeticException
• Array
• ArraySegment`1
• ArrayTypeMismatchException
• AssemblyLoadEventArgs
• AssemblyLoadEventHandler
• AsyncCallback
• AttributeTargets
• AttributeUsageAttribute
• BadImageFormatException
• Base64FormattingOptions
• BitConverter
• Boolean
• Byte
• CannotUnloadAppDomainException
• Char
• CharEnumerator
• CLSCompliantAttribute
• ConsoleCancelEventArgs
• ConsoleCancelEventHandler
• ConsoleColor
• ConsoleKey
• ConsoleKeyInfo
• ConsoleModifiers
• ConsoleSpecialKey
• Convert
• DataMisalignedException
• DateTime
• DateTimeKind
• DateTimeOffset
• DayOfWeek
• DBNull
• Decimal
• DivideByZeroException
• DllNotFoundException
• Double
• DuplicateWaitObjectException
• EntryPointNotFoundException
• EventArgs
• EventHandler
• EventHandler`1
• ExecutionEngineException
• FieldAccessException
• FlagsAttribute
• FormatException
• FormattableString
• Func`1-8
• Guid
• HashCode
• IAppDomainSetup
• IAsyncResult
• ICloneable
• IComparable
• IComparable`1
• IConvertible
• ICustomFormatter
• IDisposable
• IEquatable`1
• IFormatProvider
• IFormattable
• IndexOutOfRangeException
• InsufficientExecutionStackException
• InsufficientMemoryException
• Int16
• Int32
• Int64
• InvalidCastException
• InvalidOperationException
• InvalidProgramException
• InvalidTimeZoneException
• IObservable`1
• IObserver`1
• IProgress`1
• IServiceProvider
• Lazy`1
• LoaderOptimization
• LoaderOptimizationAttribute
• Math
• MathF
• MemberAccessException
• Memory`1
• MemoryExtensions
• MethodAccessException
• MidpointRounding
• MissingFieldException
• MissingMemberException
• MissingMethodException
• MulticastNotSupportedException
• NonSerializedAttribute
• NotFiniteNumberException
• NotImplementedException
• NotSupportedException
• Nullable
• Nullable`1
• NullReferenceException
• ObjectDisposedException
• ObsoleteAttribute
• OperatingSystem
• OperationCanceledException
• OutOfMemoryException
• OverflowException
• ParamArrayAttribute
• PlatformNotSupportedException
• Progress`1
• Random
• RankException
• ReadOnlyMemory`1
• ReadOnlySpan`1
• ResolveEventArgs
• ResolveEventHandler
• SByte
• SequencePosition
• SerializableAttribute
• Single
• Span`1
• StackOverflowException
• STAThreadAttribute
• String
• StringComparer
• StringComparison
• StringSplitOptions
• SystemException
• ThreadStaticAttribute
• TimeoutException
• TimeSpan
• TimeZone
• TimeZoneInfo
• TimeZoneNotFoundException
• Tuple
• TupleExtensions
• Type
• TypeAccessException
• TypeCode
• TypeInitializationException
• TypeUnloadedException
• UInt16
• UInt32
• UInt64
• UnauthorizedAccessException
• UnhandledExceptionEventArgs
• UnhandledExceptionEventHandler
• ValueTuple
• ValueType
• Version
• Void

Milestone II

• Activator
• Attribute
• Buffer
• Comparison`1
• Converter`2
• Enum
• Environment
• EnvironmentVariableTarget
• IntPtr
• PlatformID
• Predicate`1
• TypedReference
• TypeLoadException
• UIntPtr

Milestone III

• ActivationContext
• AppContext
• AppDomain
• AppDomainInitializer
• AppDomainManager
• AppDomainManagerInitializationOptions
• AppDomainSetup
• ApplicationIdentity
• ArgIterator
• Console
• ContextBoundObject
• ContextMarshalException
• ContextStaticAttribute
• CrossAppDomainDelegate
• Delegate
• Exception
• GC
• GCCollectionMode
• GCNotificationStatus
• LocalDataStoreSlot
• MarshalByRefObject
• ModuleHandle
• MTAThreadAttribute
• MulticastDelegate
• Object
• RuntimeArgumentHandle
• RuntimeFieldHandle
• RuntimeMethodHandle
• RuntimeTypeHandle
• WeakReference
• WeakReference`1