SerenityOS came to my attention a while back, but I had since forgotten about the project until I saw it on the front page of HN today. The project's founder Andreas Kling describes it thusly;
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.
He explains that he started tinkering with building an operating system after completing a drug rehabilitation programme. While he was the projects original sole maintainer, his efforts have blossommed into a dedicated community of contributors and testers. It's amazing to see what progress has been made in just a few short years, including (and I can't stress how mind-blowing this is to me) implementing an entire browser engine from scratch.
Kling admits that it's nowhere near "production ready" — in it's current state you have to build it from source, and it only runs in QEMU — but I absolutely love the look and feel of this OS, and I can't wait to see where the future takes it.