Valve Steam Trackball Controller
This is the trackball controller prototype by Valve, dated .

It was hyped back in 2013, as gamer wanted a input device that can have variable random speed, such as mouse or trackball.

Valve ended up with a trackpad instead. See:
They said trackpad allowed much more possibilities in configuration, for all sort of games that require novel inputs.
But i think that's a bad choice. Because:
- a trackball is a mechanical device, it allows much more accurate tracking, and the physical satisfaction of manipulating one.
- Trackpad has the fat finger problem
- It is uncomfortable to rub fingers on trackpad for long period of time
- Trackpad is unyielding, like a stone wall, it does not respond physically. It is very unsatisfactory to use. Joystick yields, button get depressed, trackball rolls, mouse moves.
- Trackpad is often inaccurate or not responsive, and user can't tell if it's lag or fat finger problem, or something else. Very annoying.
One practical problem with trackball is food crumbs or cat hairs. People will be eating potato chips on the couch, and lots trackballs will become nasty.