With UNIX having many tasks running simultaneously, through the years developers have incorporated several command-line tools that allow for live process management. These include "top", "kill", "ps", "df", and "vm_stats", and are available in the BSD subsystem in OS X via the command line. Since these tools require knowledge of the Terminal (which I admit is one of the funnest aspect of OS X), Apple has compiled the function of these and similar tools into "Activity Monitor" to make process management more user-friendly.
