The humble computer mouse celebrates its 40th anniversary today. Currently I'm using two buttons and a scroll wheel mouse. At work I've a Microsoft IntelliMouse; it has four buttons and a scroll wheel.
I think mouse helped creating modern personal computers including powerful GUI interface, email, browser etc.
From the BBC page:
On 9 December 1968 hi-tech visionary Douglas Engelbart first used one to demonstrate novel ways of working with computers.
The first mouse that Dr Engelbart used in the demo at the Fall Joint Computer Conference (FJCC) was made of wood and had one button.
Much of the technology shown off in the demo inspired the creation of the hardware and software now widely used.