AppImage is a software tool that helps creating standalone application under Linux.
The key idea of the AppImage format is one app = one file. Every AppImage contains an app and all the files the app needs to run. In other words, each AppImage has no dependencies other than what is included in the targeted base operating system(s).
Using AppImageKit you can package desktop applications as AppImages that run on common Linux-based operating systems, such as RHEL, CentOS, Ubuntu, Fedora, Debian and derivatives.
The AppImage format is a format for packaging applications in a way that allows them to run on a variety of different target systems (base operating systems, distributions) without further modification.
AppImageKit is a concrete implementation of the AppImage format and provides tools for conveniently handling AppImages.