GaryOS is an entire GNU/Linux system in a single bootable file.
While most boot/rescue systems use an ISO with SquashFS, GaryOS is a single binary file consisting of a Linux kernel and a Funtoo/Gentoo initramfs. The file is generated using a customized Funtoo/Gentoo configuration with a default Grml Linux kernel configuration via the Metro automated build tool.
There are currently no major projects which take this same approach on this scale. The result is a smaller boot/rescue file that is just as comprehensive, yet easier to deploy and manage.
GaryOS enables you to drop a single file on any media, point a bootloader at it and go. Upgrades are as simple as replacing the file and/or adding another bootloader entry.
Rescue media is more likely to be available and up-to-date if it is convenient to deploy and manage, which is one of the primary aims of GaryOS.