Auto Clicker is a System Utilities software developed by Valis Enterprises. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Auto Clicker:

Configure your mouse to AutoClick, fully customizable: interval, clicks, pauses, button, etc.

You can choose to automatically click your left , Middle and right mouse button, set the interval at which the clicks will occur, set pauses between clicks, automatically stop after a desired ammount of clicks.
You can also stop the clicks at any time pressing the ESC key

New in version 2: "Random autostop delays", you can set the AutoClicker to pause the clicking for X miliseconds, where X is a random value from a list of delays created by the user, or randomly generated by clicking "Generate random delays".