"SerenityOS is a love letter to '90s user interfaces with a custom Unix-like core. It flatters with sincerity by stealing beautiful ideas from various other systems.
Roughly speaking, the goal is a marriage between the aesthetic of late-1990s productivity software and the power-user accessibility of late-2000s *nix."
I think in terms of paradigm, Serenity has a stronger ideology than RedoxOS. It brings BeOS and Mac concepts like a consistent and fully integrated monorepo system and development kits, and a very strong and defined user interface paradigm.
From that perspective I find Redox much less of a paradigm for the end-user, if the main feature is the language the developers used. Orbital does not look remarkable.
The level of productivity of Andreas himself, his videos and the community he managed to built, including growing a few individuals of to major contributors to the point they created a whole browser stack is just outstanding as an open-source case study. Also to me, much more interesting than a programming language used to built it.
Haiku is written in the same language as Serenity, btw.