Borland used the name "Object Pascal" for the programming language in the first versions of Delphi, but later renamed it to the "Delphi programming language". However, compilers that claim to be Object Pascal compatible are often trying to be compatible with Delphi source code.
Note that today Object Pascal is used collectively to refer to different dialects of the Pascal language with object-oriented programming extension, although these dialects are more or less compatible with CodeGear's implementation.
Object Pascal was needed in order to support MacApp, an expandable Macintosh application framework that would now be called a class library. Object Pascal extensions and MacApp itself were developed by Barry Haynes, Ken Doyle, Larry Rosenstein, and tested by Dan Allen. Larry Tesler oversaw the project, which began very early in 1985 and became a product in 1986.
Apple dropped support for Object Pascal when they moved from Motorola 68K chips to IBM's PowerPC architecture in 1994.
Object Pascal extension also have been implemented in the Think Pascal IDE. The IDE includes not only the compiler, but also an editor with Syntax highlighting and checking, a very powerful debugger and a class library. Many developers preferred Think Pascal instead of MacApp because it offered a tight integration of its tools. The development stopped after the 4.01 version, because the company was bought by Symantec. The developers then left the project.
The Borland and CodeGear years
In 1986, Borland introduced similar extensions, also called Object Pascal, to the Turbo Pascal product for the Macintosh, and in 1989 for Turbo Pascal 5.5 for DOS.
When Borland refocused from MS-DOS to Windows in 1994, they created a successor to Turbo Pascal, called Delphi and introduced a new set of extensions to create what is now known as the Delphi language.
The development of Delphi started some time in 1993 and Delphi 1.0 was officially released in the US on 14 Feb 1995. While code using the Turbo Pascal object model could still be compiled, Delphi featured a new syntax using the keyword class in preference to object, the Create constructor and a virtual Destroy destructor (and negating having to call the New and Dispose procedures), properties, method pointers, and some other things. These were obviously inspired by the ISO working draft for object-oriented extensions, but many of the differences to Turbo Pascal's dialect (such as the draft's requirement that all methods be virtual) were ignored.
There are many compilers that are more or less compatible with the Object Pascal language from Delphi. Many of these were created to enable the use of Object Pascal source code on different platforms, and under various licenses.
Borland Kylix is a Linux variant of Delphi, and only targets Intel 32-bit Linux using Qt. It is not updated anymore and starting to show its age. Modern distributions often do not work out of the box with this tool.
Free Pascal is a command-line compiler aimed at source compatibility with the core feature set of both the Turbo Pascal and the Delphi dialects. The current version, 2.2, is highly Delphi6/7 compatible. FPC generates code for x86, AMD64, PowerPC, SPARC and ARM processors under various operating systems, including Win32, Win64, Linux, FreeBSD, Mac OS and Mac OS X (including an Xcode integration kit). Beyond command-line usage, several development environments are available for Free Pascal, in particular the Lazarus IDE.
GNU Pascal (A separately distributed part of the GNU Compiler Collection) While formally not aimed at the CodeGear dialects of Pascal, it does contain a Borland Pascal compatibility mode, and is very slowly incorporating a few Delphi language features. It is not suitable for recompiling large bodies of Delphi code directly, but is noteworthy as having prolific support for operating systems and hardware architectures.
Virtual Pascal is a x86 32-bit Turbo Pascal and Delphi compatible compiler aimed mainly at OS/2 and Windows, though it developed a DOS+ Extender and an experimental Linux cross-compiler too. The compiler is stuck at about the level of Delphi V2, the site has been down for nearly one and a half year now, and development of Virtual Pascal has stopped. Nevertheless, of the free alternatives, it is still the one with the best polished IDE and debugger, though Free Pascal is catching up.
Oxygene (formerly known as Chrome) is an Object Pascal compiler from RemObjects Software that integrates into Visual Studio. It is also available as free command-line compiler that runs native on .NET/Mono. It targets the .NET and Mono platforms.
Pascal Script (formerly known as InnerFuse) is an open source Object Pascal interpreter/scripting engine written in Delphi. Supports a limited subset of Object Pascal.
Sample "Hello World" programs
Apple's Object Pascal
Turbo Pascal's Object Pascal
Delphi And Free Pascal's Object Pascal
Note that the object construct is still available in Delphi and Free Pascal (Delphi-compatible mode).
Oxygene Object Pascal
Many features have been introduced continuously to Object Pascal with extensions to Delphi, now also by Free Pascal. In reaction towards criticisms, Free Pascal has adopted generics, and both Delphi and Free Pascal now supports operator overloading (with different grammar, though). Delphi has also introduced many other features since version 7.
Object Pascal in the software market
Although C# and Java dominate the software industry market, Delphi has a considerable market share and strong presence.