First: Programs use diffrent libraries: shared, linked and static. Comparise efficiency, also using diffrent options on compiler.
Second: Comparise systems functions to operate on files and from "stdio.h" Using functions for directories.
Third: Basic usage of processes. Interpreter.
Fourth: Using signals.
Fifth: Using pipes.
Sixth: Message queues. Better interpreter.
Seventh: Shared memory, semaphores. Sleeping barber problem.
Eigth: Threads. Filter.
Nineth: Threads synchronisation. Producers and consuments problem.
Tenth: Using sockets: Datagram and stream; unix and ip4