I've released the first 'official' version of MikeOS, a 16-bit PC OS written in assembler. MikeOS isn't planned to be a general-purpose OS, but more of a learning tool for those wanting to write a basic OS and learn x86 assembly. It includes FAT12 support, a bunch of system calls, and rudimentary DOS compatibility.
Homepage: http://mikeos.sourceforge.net
The biggest feature of this release is the Handbook, a complete guide to running, building and modifying the OS:
http://mikeos.sourceforge.net/handbook.html
But perhaps of most interest to forumers here, I've included a whole section on writing your own OS, with mini primers on PC booting and x86 assembler. It covers the basics and shows how to get a simple (bootloader) OS running:
http://mikeos.sourceforge.net/handbook.html#makeintro
It's really compacted, but hopefully a useful source of info to point OS first-timers at on the forums. I've tried to keep the boring gunk to a minimum whilst getting newcomers up-and-running quickly

Any comments or suggestions, I'd love to hear them!
Thanks all,
Mike