AutoIt is a freeware BASIC-like scripting language designed for automating the Windows GUI and general purpose scripting.
It’s mainly used to simulate keystrokes pression and mouse move, the creation of messages and input windows. AutoIt is also used to create complex Windows GUI (Graphic User Interface) from simple buttons to dropdown menus, checkbox, radiobuttons, labels and so on…
The .au3 scripts can be compiled as executable so can be used standalone in any pic without the program installed (thanks to the Aut2Exe included utility), they can be created with the built in SciTE Script Editor with syntax highlighting
The powerful scripting language offers many possibilities like download files from internet, reproduce mouse clicks, create macros and many more.
If you want to start with it there is a very good online documentation, a wiki and a support forum.
Moreover if you wanna study there are also some examples created by AutoIt forum members.