Pretorian Technologies of Lincolnshire, UK http://www.pretorianuk.com/ specializes in computer devices for disabled, and semi-disabled users. They make a wide variety of trackballs, joysticks, mouse alternatives, big switches that can be activated by your elbow or knee, iPad switches, bluetooth linked switches etc.
Their devices are aimed at those with "limited hand control, fine and gross motor skill difficulties, poor hand-eye coordination, limited manual dexterity, repetitive strain injury, involuntary muscle spasms, spastic and flaccid paralysis, cerebral movement disorder or central neuromuscular disability and inflammatory or degenerative change"
From their website, http://www.pretorianuk.com/n-a...
The n-ABLER Trackball is the most adaptable Mouse Alternative on the market specifically designed to address the needs of computer users with limited hand control, motor skill difficulties, poor hand-eye co-ordination, lack of manual dexterity and involuntary muscle spasms.
In the USA, their products are available through InclusiveTLC.com