Action! is a programming language, with integrated editor, debugger, and 6502 compiler, for the Atari 8-bit family of microcomputers. Action! was created by Clinton Parker and released on cartridge by Optimized Systems Software in 1983. Its syntax is similar to that of ALGOL 68.
Action! is significant for its high performance, which allows games and graphics demos to be written in a high-level language without use of hand-written assembly language code. Action! language constructs were designed to map cleanly to 6502 opcodes.
A development library was available as a separate product called the Action! Toolkit. Action! was used to develop at least two commercial products: the Homepak productivity suite and Games Computers Play client program. The language was never ported to other systems.
In 2007 it inspired Effectus - a cross-compiler currently running on Windows targeting the Atari 8-bit. Effectus resembles Action! syntax and is intended to be as compatible as possible with it.