MicroEmpix

MicroEmpix is the microkernel version of Empix, an operating system developed at the Computing Systems Laboratory of the Electrical & Computer Engineering department at the National Technical University of Athens.
Empix began in the late 1980s as the laboratory's effort to write a small Unix-like modern multitasking OS, intended for educational use. Borrowing most of its basic characteristics from other popular OSes of the time. Empix is quite small and supports Intel x86 processors, in the IBM Personal Computers XT, and AT architectures, floppy disks and hard disk drives, and Enhanced Graphics Adapter graphics and the serial ports. It has a shell with some basic commands, and the ability to execute multiple processes.
MicroEmpix is far different. It's about 1,600 lines of code, and it's a microkernel, meaning that it creates and runs processes in kernel-space, with no distinction between process-space and kernel space. What the kernel sees, the process sees and vice versa. No system calls occur to require a system call dispatcher or a similar mechanism. Kernel functions are inherent to the processes created, and there is but one user.