Kurt Skauen is both a video game programmer for Empire Interactive Entertainment and the sole developer of the AtheOS operating system. He created a full OS from scratch, and designed - all by himself - the kernel, GUI, and the OOP C++ API. AtheOS is a modern open source OS, fully usable.
Here is what Kurt had to say about AtheOS.
It's nice to see that people are interested in the project but I don't feel responsible to deliver anything in particular. If giving away something automatically meant you where responsible to fullfill all demands from everybody who accepted the gift I don't think there would be many free software projects out there. If people like AtheOS that's great but if they don't there is a lot of other OS's out there to save their day. If none of them fit they can always write their own.