We've seen eye-tracking systems that help determine the preferences of shoppers or website browsers. Here's one that could really benefit people who suffer from physical limitations: The EyeWriter project.
It's an ongoing collaborative research effort to empower people who are suffering from amyotrophic lateral sclerosis (ALS; aka Lou Gehrig's disease) with creative technologies. It allows graffiti writers and artists with paralysis resulting from ALS to draw using only their eyes.
The collaborative consists of members of Free Art and Technology (FAT), OpenFrameworks, the Graffiti Research Lab, and The Ebeling Group communities. They have teamed-up with LA graffiti writer, publisher, and activist, Tony Quan, aka TEMPTONE. He was diagnosed with ALS in 2003, a disease which has left him almost completely physically paralyzed… except for his eyes.
The long-term goal is to create a professional/social network of software developers, hardware hackers, urban projection artists and ALS patients from around the world who are using local materials and open source research to creatively connect and make eye art.