AppImage (formerly known as klik and PortableLinuxApps) is an open-source format for distributing portable software on Linux.

It aims to allow the installation of binary software independently of specific Linux distributions, a concept often referred to as upstream packaging.

For the main ingredients, pre-built .deb packages from Debian Stable repositories were usually fed into the recipe's generation process.

With klik, only eight programs could be run at once because of the limitation of mounting compressed images with the Linux kernel, unless FUSE was used.

The next version, klik2, was in development and would natively incorporate the FUSE kernel module, but it never reached past the beta stage.

[4] Simon Peter started a successor project named PortableLinuxApps with similar goals around that time.

AppImage is designed to be simpler to use than traditional installer formats such as Deb and RPM, since it is not necessary to modify the operating system or user environment.

A version 1.0 AppImage is an ISO 9660 Rock Ridge file (which can be optionally compressed via zisofs) containing a minimal AppDir and a runtime.