postmarketOS (pmOS), is a touch-optimized, pre-configured Alpine Linux that can be installed on smartphones and other mobile devices. The project is at very early stages of development and is not usable for most users yet.
We develop a sustainable mobile OS
It is 2017. Pick an average PC from 2007 and install a minimal Linux based operating system. You will be able to do basic computing tasks (eg. surfing the web, reading e-mails, listening to music, chatting) just like on an expensive modern PC. You will even get security updates, so your old computer is protected, just like a new one.
On the current mobile landscape you get none of that. Even expensive phones only have few years of support. As time progresses, your phone becomes slower and slower, and the newest features will not work on it anymore. But postmarketOS builds upon a real Linux distribution, which has no reason to drop support for old devices at all and (assuming that you choose the right software) keeps the resource usage at a constant minimum instead of increasing it with every release. There's no reason to restrict features (such as full disk encryption) to newer devices either. We want to be able to use our devices until they break!
Package and run anything you want
postmarketOS is developed in the spirit of regular Linux distributions, so there's no problem in having multiple phone interfaces (e.g. UBports, featurephone with big numbers, plain shell) and let the user choose. A lot of work already went into getting KDE plasma mobile running, it is getting closer every day!
Furthermore postmarketOS will not impose arbitrary restrictions on you. Use the apps from any ecosystem you want (even desktop software). With Alpine's simple package format, you do not need more than a bit of Linux knowledge to package your favorite programs (assuming that they run on Linux already).