A simple operative system I created some years ago in order to learn more about computers.
This project is based on the kernel tutorials by JamesM (http://www.jamesmolloy.co.uk/tutorial_html/index.html) and Brandon F (http://www.osdever.net/bkerndev/index.php), and the really helpful OSDev.org wiki and forums.
Last things I added were a simple command line interface and a very basic VGA driver (not finished).
Once built, it includes a makefile, you can use QEMU to test it: qemu-system-i386 -kernel oskernel -soundhw pcspk