List of Delphi language features and version in which they were introduced/deprecated

Note that this answer only lists new language features

Here are the links to the RAD Studio docwiki:
- What's new in Delphi and C++Builder 10 Seattle
- What's new in Delphi and C++Builder XE8
- What's New in Delphi and C++Builder XE7
- What's New in Delphi and C++Builder XE6
- What's New in Delphi and C++Builder XE5
- What's New in Delphi and C++Builder XE4
- What's New in Delphi and C++Builder XE3
- What's New in Delphi and C++Builder XE2
- What's New in Delphi and C++Builder XE
- What's New in Delphi and C++Builder 2010
- What's New in Delphi and C++Builder 2009
- What's New in RAD Studio (Delphi for Win32 2007)
- What's New in RAD Studio (C++Builder 2007)
- What’s New in Delphi 2006
- What’s New in Delphi 2005
- What’s New in Delphi 7
- What’s New in Delphi 6
- What’s New in Delphi 5
- What's New in Delphi 3

The full list from Embarcadero: What's New
See also: David I's list

To summarize:

Delphi 10 Seattle

• Support for Android 5.1.1 and iOS 8.4
• Improved OSX exception handling

Delphi XE8

• Support for 64-bit iOS;
• New integer types: FixedInt, FixedUInt 32-bit integer types on all platforms;
• New platform dependent integer types: LongInt, LongWord (64-bits on iOS-64, 32-bits on all other platforms);
• Fully qualified names must now include the unit scope name

Delphi XE7

• String-Like Operations Supported on Dynamic Arrays
• Parallel Library added to the RTL

• New compiler intrinsic routines (undocumented):

  function IsManagedType(T: TypeIdentifier): Boolean; function HasWeakRef(T: TypeIdentifier): Boolean; function GetTypeKind(T: TypeIdentifier): TTypeKind; function IsConstValue(Value): boolean;

Delphi XE6

• Enum identifier names have no prefixes.

Delphi XE5

• Android Support;
  needs device with ArmV6 + Neon or ArmV7 for deployment
  introduces conditional define ANDROID
• Operator overloading for classes (but only for the NextGen compiler {Android/iOS})

Delphi XE4

• The following new conditionals are introduced/enabled in XE4:
  AUTOREFCOUNT
  CPUARM
  EXTERNAL_LINKER
  IOS
  NEXTGEN
  UNDERSCOREIMPORTNAME
  WEAKREF
  WEAKINSTREF
  WEAKINTREF

  • Reintroduced support for iOS.
  • ARC support in NextGen compilers (including TObject.DisposeOf).
    _{Note that much of the groundwork for ARC was already in XE3, but much of it was disabled}

Delphi XE3

• Record helpers for built-in types
• Removed support for iOS.
• Atomic intrinsic functions:
  AtomicExchange(), AtomicIncrement(), AtomicCmpExchange(), AtomicDecrement()

Delphi XE2

• Cross platform support for Mac OSX (32-bit) and iOS;
• Support for Win64;
• Modified RTL to support cross platform;
• Packed Now Forces Byte Alignment of Records (Pre XE2 it did not necessarily do this)

• Eight new DEFINEs have been added:

  ALIGN_STACK
  CPUX86
  CPUX64
  MACOS (Mac operating system)
  MACOS32
  PC_MAPPED_EXCEPTIONS
  PIC
  WIN64

• Full unit scope names are now required in your uses clause.
• The build-in types differ depending on the target platform (32/64-bit)
  • Extended Data Type Is 10 bytes on Win32, but 8 (!) bytes on Win64

Delphi XE

• The {$STRINGCHECKS} compiler directive is ignored in XE;
• New 16-byte value for the {$ALIGN} directive: The acceptable values for the {$ALIGN} directive now include 1, 2, 4, 8, and 16.
• new {$CODEALIGN} directive, this sets the starting address for a procedure or function.
• The {$STRONGLINKTYPES ON} directive
• Support for regular expressions.

Delphi 2010

• Enhanced Delphi RTTI (Run Time Type Information).
• Attributes
• The as operator can be used to cast an interface reference back to the object from which it was extracted.
• The is operator can be used to verify whether an interface reference was extracted from a certain class.
• Normal unsafe casting can be performed on an interface: TObject(SomeInterface).
• new delayed directive indicates that an external library such as a DLL is not to be loaded at declaration time but is to wait until the first call to the method
• Class Constructor/Destructor

Delphi 2009

• Intrinsic type string now maps to UnicodeString;
• Generics;
• function Default(T): T intrinsic function (Undocumented)
• Smart pointers;
• Anonymous methods;
• Support for nested exceptions and exception tracing;
• support for pointermath and a new compiler directive: {$POINTERMATH ON|OFF};
• Four new compiler warnings:
  • W1057 Implicit string cast from '%s' to '%s',
  • W1058 Implicit string cast with potential data loss from '%s' to '%s',
  • W1059 Explicit string cast from '%s' to '%s',
  • W1060 Explicit string cast with potential data loss from '%s' to '%s';
• The Exit function can take a parameter specifying a result;
• resourcestrings as Widestrings;
• TObject has a extra hidden pointer to TMonitor in addition to its VMT pointer;
• the deprecated keyword can now have additional text

Delphi 2007

• No language changes that I know of;
  Note that Delphi 2007 is a non-breaking release, DCU's from D2006 will work unchanged in D2007;
• (The .NET 'personality' of 2007 introduced generics)

Delphi 2006

• Enhanced records;
• operator overloading;
• static methods and properties;
• class helpers;
• FastMM is the default memory manager;
• strict private/protected visibility keyword;
• final keyword for virtual methods;
• {$METHODINFO} directive;

Delphi 2005

• for ... in loops,
• inline keyword
• Wildcard in uses statement allowed
• nested types
• nested constants
• {$REGION}/{$ENDREGION} directives

Delphi 7

• three additional compiler warnings:
  • Unsafe_Type,
  • Unsafe_Code, and
  • Unsafe_Cast. These warnings are disabled by default, but can be enabled
• new compiler directive {$WARN UNSAFE_CODE ON}
• Overloads of routines that format and parse numbers, date-time values, and currency using a TFormatSettings structure.

Delphi 6

• New compiler directives:
  • {$IFDEF MSWINDOWS}
  • {$IFDEF LINUX}
    [- {$LIBPREFIX}
  • {$LIBSUFFIX}
  • {$LIBVERSION}]52
  • {$MESSAGE 'message'}
  • {$SetPEFlags}
• Support for {$IF}{$ELSE} compiler directives
• Compiler hinting directives: experimental, deprecated, library, platform (but without additional text for deprecated)
• Variant is no longer based on COM but changed to be CLX compatible, COM based variant renamed to OLEVariant
• Typed constants cannot be assigned to (Override with {$J+})
• Enumerated types can be assigned an explicit value (cf C++);
• Interface properties
• Support for calling varargs external functions (but only for the cdecl calling convention)
• custom variants

Delphi 5

No new language features, but:

• Support added for Frames

Delphi 4

• Dynamic arrays
• LongWord and Int64; Cardinal is an UINT32 (before it was unsigned 31-bit value)
• Real takes 8 bytes and is the same as double (previously it was 6 bytes);
  • Override with the new {$REALCOMPATIBILITY ON} compiler directive;
  • REAL48 replaces the old 6-byte real;
• Support for resourcestrings
• Method overloading
• Default parameters
• {$EXTERNALSYM} and {$NODEFINE} directives
• implements keyword for properties

Delphi 3

• Wordbool, longbool and bytebool store false as -1 instead of 1 (Boolean is unchanged)
• Components must be installed using packages.
• Assertions.
• out parameters.
• Widestring
• interface and dispinterface keyword and COM (dispid) support.

Delphi 2

• Support for 32-bit;
• Ansistring replaces shortstring as the default string type
• Currency
• Variant (for interop with OLE automation).
• Threading support and ThreadVar keyword.
• 4 byte data is 4 byte aligned new packed keyword overrides this behavior;
• TDateTime starts at 1899/12/30 under D1 it started at 0000/00/00
• new finalization keyword
• register and stdcall calling conventions added.
• packed keyword.