Steam Controller ^_^
It works quite well with the SC Controller software on GNU/Linux desktop.
Okay, right now I'm typing, though, and not gripping the controller; I have a CST L-Trac next to the keyboard.
Before that, I used the built in pointing devices in my thinkpad, i.e., a genuine trackpoint and a T450 trackpad, or a Mionix Avior SK in the office (I've also bought another Roccat Kova 2016 to enjoy EasyShift both at home and in the office).