Qwriting

Qwriting offers an alternative on-screen keyboard for people who want to use
a mouse to type. It is particularly useful for people who don't want to move
the mouse around much - e.g. people with good fine motor control but without
very good 'gross' control (e.g. possibly people with Spinal Muscular Atrophy,
Motor Neurone Disease, Muscular Dystrophy...). 

Website:
http://www.oatsoft.org/Software/qwriting