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 people yet.
Creating a sustainable mobile OS
It is 2018. Pick an average PC from 2008 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!
This is a really interesting idea. My old Moto G is partially supported right now, so hopefully this will be something fun to play with at some point.