I'm less interested in the OS than the browser - though it may be interesting to see where it goes, and reassurring to have another backup in the event of Linux and BSD OSes becoming unworkable - but yeah, one of the points of Serenity seems to be about being [mostly] self-contained, so it has its own kernel, but also its own and window manager/server/etc.

On one hand they may be spending time re-inventing the wheel, but at the same time there's merit in having a consistent self-contained system with understandable code.

(I had a look at Serenity's code for "mkdir" command, there's no stupid comments there, and it is concise and comprehensible despite me not being a C/C++ developer. The same is not true for other mkdir implementations.)