System Activity is akin to the Microsoft Window's Task Manager, Apple's Mac OS X's Activity Monitor and Gnome's System Monitor.
It shows a list of currently running processes, along with their CPU usage, Memory usage, and various other pieces of information.
The kernel, and other tools, can provide a lot of information about a process, such as the libraries that it pulls in, how the memory is laid out, and so on. Using scripting, we can present this information in an easy to read format.
If the user right clicks on a process, they get a context menu similar to:
If you write an interesting script, and want to have it included with KDE, please email it to me at email@example.com.