Obligatory mention of Sailfish OS.

Website: https://sailfishos.org/

Main forum: https://forum.sailfishos.org/

Recently on HN: https://news.ycombinator.com/item?id=47216037 / https://news.ycombinator.com/item?id=47311456 / https://news.ycombinator.com/item?id=41749296