Hello Rose,
What exactly do you mean by special needs? There is a lot of free, educational software online. If your students are cognitively challenged then you might be able to use pre-school or kindergarten applications.
I once made a special IR pen for students with severe muscle control challenges. This pen was moved on a letter or a choice board by a teacher while a large (game show style) puncher button was place on the desk in front of the student. When the IR rod was hovering over the item of choice, the student would push down on the button and the item would activate.
Another way this system could possibly help is to develop a software that expects a user to stay on a certain path and work their way from a start point to a finish point. This can be timed, and a celebration animation could be added if the course is completed successfully. Then as skill and muscle strength improve, the course could be made more difficult.
If you have any other ideas yourself, I love to take on new challenges.
James.