Data file that describes a character created for Microsoft Agent, an interactive animation program; contains character data that can be loaded over the HTTP (or Web) protocol; saved along with a corresponding .ACA file, which contains animation data for the character.

NOTE: Microsoft Agent has been discontinued with the release of Windows 7.

An ACF file is a cache file used by Valve Steam, a software package used for downloading games. It saves information related to the downloaded software and is used for the original download as well as game updates.

ACF files are used by newer versions of the Steam content delivery system. Older versions use .GCF and .NCF files.

Aircraft file used by X-Plane, a realistic flight simulator for pilots and simulator hobbyists; contains data that describes the properties of the aircraft, such as engine power, flight physics, mass properties, and limits.

You can create an ACF file using Plane-Maker, which is a utility that comes with X-Plane. However, Plane-Maker does not enable you to create a 3D model, it is only used to determine the layout of basic aerodynamic shapes and properties of the aircraft. You can use the AC3D application with the X-Plane plugin to create a 3D model in the X-Plane OBJ format. NOTE: Before version 10 of X-Plane, the ACF file contained aircraft data in binary format. It now contains data in text format.