I work on a hobby operating system. I have 3 major projects at this point, called Codename Spectrum, YAOS, and Codename Proton.
Spectrum was my first kernel, based heavily off an online tutorial. I didn't do much with it, but it ended up with a small shell and a selection of commands.
YAOS is a redo, standing for Yet Another OS. It doesn't have a shell or anything, it functions much more on kernel capabilities than on the user.
In fact, it doesn't give any user interface, but it did finish implementing interrupts, and has timer functionality.
Finally, Proton was an attempt at creating something similar to DOS, but it never quite worked out, due to the difficulties of writing pure assembly.