Click2Speak is a full-featured virtual keyboard with desktop access and brilliant predictive text in several languages. It was co-created by the late Gal Sont a developer with MND (ALS) who used eye gaze to write the code.
The software includes built-in support for the new breed cheap eye gaze cameras - Tobii Gaming . Standard mice, head trackers or other eye gaze devices with mouse emulation can also be used.
Support for switch access is currently in development.
It's a great free package for literate eye gaze users which additionally provides access to desktop software and external devices like TVs and STBs (using a cheap IR remote extension).