From the link:
We are sick of not receiving updates shortly after buying new phones. Sick of the walled gardens deeply integrated into Android and iOS. That’s why we are developing a sustainable, privacy and security focused free software mobile OS that is modeled after traditional Linux distributions. With privilege separation in mind. Let’s keep our devices useful and safe until they physically break!
TL;DR A Linux distro for smartphones that no longer receive manufacturer support. It’s lightweight and firmware support comes straight out of the box.
The project is still in alpha so expect bugs and spotty support.