appimagetool vs install4j

appimagetool is a free Linux command-line utility that creates an AppImage from an existing AppDir. It is intended for application authors packaging desktop Linux software for distribution across common Linux distributions. The project describes it as a low-level component and recommends community higher-level tools for most users. Command-line options cover listing AppImage files, setting or guessing update information, selecting Squashfs compression, and excluding files. GPG signing is supported with a signing key and additional arguments. When update information is embedded and zsyncmake is installed, the tool can create a zsync file. Build instructions list x86_64, i686, aarch64, and armhf targets. The current version downloads the latest AppImage runtime, or accepts a local runtime file. Update information can be guessed from GitHub Actions and GitLab CI environment variables. An AppDir is required, and ARCH must be set when binary architecture cannot be determined, such as with multiple architectures or shell scripts. Source code is under the MIT License, subject to stated exceptions and dependency terms.

install4j has no write-up on Specifiction yet; its figures are above.