SerenityOS

SerenityOS is a free and open source desktop operating system. It features a preemptive kernel, currently supports x86-64, ARM, and RISC-V based computers, and hosts multiple complex applications including its own web browser and integrated development environment (IDE).

SerenityOS began development in 2018 as a solo project by Swedish programmer Andreas Kling. It is maintained by a community of hobbyists on GitHub where it is described as "a love letter to '90s user interfaces with a custom Unix-like core" that "does not cater to non-technical users". Provided by Wikipedia