postmarketOS is described as 'Extends the free and open source operating system Alpine Linux to run on smartphones and other mobile devices. Alpine is a security-oriented, light-weight Linux distribution based on musl libc and BusyBox' and is a popular Mobile OS in the os & utilities category. There are more than 25 alternatives to postmarketOS for a variety of platforms, including Android, Linux, Linux Mobile, Android Tablet and Self-Hosted apps. The best postmarketOS alternative is Android, which is both free and Open Source. Other great apps like postmarketOS are GrapheneOS, LineageOS, iodéOS and /e/.