I'm just interested: I would like to hear about your OS's system calls (if they are special).
What syscalls do you have that differ from Windows/POSIX/Linux/BSD?
Here I count as syscalls both kernel and base library functions (like libc for example).
Those could be
a) a different method for the usual funcionality (for instance process managment done in your own special way)
or b) area which is not covered by normal OS (could be security or multimedia etc.)
To name two examples:
1.) Amiga OS had the functionality to forbid and permit multitasking.
2.) A distributed OS has intra-kernel and inter-process communication differing from normal OS.
Happy hacking
Peter