The AppImage format is complemented by a suite of tools called AppImageKit that provide a concrete sample implementation of the ideas expressed in the format, and that can greatly simplify dealing with AppImages.
Currently the AppImageKit contains (among others)
create-appdir, a command line tool running on Ubuntu that turns packaged software into AppDirs. This tool can be used to semi-automatically prepare AppDirs that can be used as the input for AppImageAssistant. Note that while create-appdir has been written for Ubuntu, it should also run on debian and could be ported to other distributions as well, then using the respective package managers insted of apt-get.
AppImageAssistant, a GUI app that turns an AppDir into an AppImage.
AppRun, the executable that finds and executes the app contained in the AppImage. create-appdir automatically embeds AppRun into the AppDirs it creates.
runtime, the tiny ELF binary that is embedded into the header of each AppImage. AppImageKit automatically embeds the runtime into the AppImages it creates.
AppImageKit also contains additoinal tools and helpers.