Graphic Adventure Creator (often shortened to GAC) is a game creation system/programming language for adventure games published by Incentive Software

Incentive Software

Incentive Software Ltd. was a British video game developer and publisher founded by Ian Andrew in 1983. Programmers included Sean Ellis, Stephen Northcott and Ian's brother Chris Andrew. Later games were based around the company's Freescape rendering engine...

, originally written on the Amstrad CPC

Amstrad CPC

The Amstrad CPC is a series of 8-bit home computers produced by Amstrad between 1984 and 1990. It was designed to compete in the mid-1980s home computer market dominated by the Commodore 64 and the Sinclair ZX Spectrum, where it successfully established itself primarily in the United Kingdom,...

 by Sean Ellis, and then ported to other platforms by, amongst others, Brendan Kelly (Spectrum), Dave Kirby (BBC, Electron) and "The Kid" (Malcolm Hellon) (C64). The pictures in the demo adventure, Ransom, were made by Pete James and the box cover art by Pete Carter.

GAC was available for the ZX Spectrum

ZX Spectrum

The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...

, Commodore 64

Commodore 64

The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...

, BBC Micro

BBC Micro

The BBC Microcomputer System, or BBC Micro, was a series of microcomputers and associated peripherals designed and built by Acorn Computers for the BBC Computer Literacy Project, operated by the British Broadcasting Corporation...

 and Amstrad CPC

Amstrad CPC

The Amstrad CPC is a series of 8-bit home computers produced by Amstrad between 1984 and 1990. It was designed to compete in the mid-1980s home computer market dominated by the Commodore 64 and the Sinclair ZX Spectrum, where it successfully established itself primarily in the United Kingdom,...

. A simplified version without graphics, called just the Adventure Creator, was also available for the Acorn Electron

Acorn Electron

The Acorn Electron is a budget version of the BBC Micro educational/home computer made by Acorn Computers Ltd. It has 32 kilobytes of RAM, and its ROM includes BBC BASIC along with its operating system....

. GAC was later ported to the Atari ST

Atari ST

The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...

 as ST Adventure Creator (STAC).

GAC had a more advanced parser than The Quill

The Quill

The Quill is a program to write home computer adventure games. Written by Graeme Yeandle, it was published on the ZX Spectrum by Gilsoft in December 1983...

, allowing commands like GET THE LAMP THEN LIGHT IT, and a built-in graphics editor. Over 117 titles were written using GAC. It also came with a built in text compressor.

The Graphic Adventure Creator used the Lenslok

Lenslok

Lenslok is a copy protection mechanism found in some computer games and other software on the 8bit Atari, Commodore 64, Sinclair ZX Spectrum, Sinclair QL, MSX and Amstrad CPC. The most famous game to use it was Elite for the ZX Spectrum....

copy protection system.