[1.6] Multitasking will that mean....

that we can have several programs running in the computer? So I can make a program that listen on the network and another program doing ex. controlling my power setup - all on one computer?

Yes.

It was already possible with the parallel API or couroutines, but now it's included in the shell.

Note however, you can't run two things at the same time in lua, you can just get the same effect by quickly swapping between different coroutines. Computercraft computers also don't run at the same time, they run quickly after each other.