Call the trackball the recumbent bicycle of pointing devices: arguably superior (no mouse pad required!), beloved by a few weirdos, but never a mainstream hit (except, of course, when mounted inside a Missile Command console). I count myself among the weirdos–I used a wonderfully ambidextrous, sturdy Kensington Expert Mouse like this one for years. It’s a testament to the universal acceptance of Engelbart’s invention that Kensington calls this a mouse despite the fact that it isn’t one. (The company makes a modern version to this day.)  (Image from Leedsmet.)