Monarchy Linux was a source-based Linux distribution active primarily in the early 2000s. It was essentially an automated version of Linux From Scratch (LFS).
Palm OS defined the PDA category and pioneered the concept of the smartphone. Its focus on speed and core productivity remains influential
MeeGo was a promising, unified OS that was killed by corporate strategy before it could flourish, but its technology and ideas lived on in other projects
postmarketOS (pmOS) is a free, open-source Linux-based operating system designed for mobile devices like smartphones and tablets.
Motorola's OS history mirrors the entire mobile industry's evolution, from simple proprietary software to the modern smartphone era
Maemo was a pioneering, Linux-based open-source operating system developed by Nokia in the mid-2000s for its "Internet Tablets" and smartphones.