Yay! I'm all caught up :).
16. Find a problem that might affect someone who can’t use their hands.
This is a broad range of issues that falls under the umbrella term "motor disabilities" and can have many possible causes. We can be talking about the limited use of limbs due to paralysis, deformities, prosthetics, and in cases where there is no limb to use. Due to these limitations, there are several instances that can be looked at as barriers to interacting with technology, as well as a number of devices that can help with overcoming those limitations.
I remember as a child seeing a news program that celebrated a local resident who had lost the use of her arms due to an accident. She was a talented artist, and rather than give up her skills, she trained herself to use her mouth and her head movements to replace the motor control that her arms and hands used to provide. Yes, for those curious, she resumed painting by holding a paintbrush in her mouth. In many ways, that analog is used today by many with motor disabilities, where the head and neck, eyes, chin, and mouth are utilized to make up for the loss of hands as primary input devices.
WebAim has a page that is dedicated to assistive technology alternatives for those with motor disabilities. These range from simple sticks that can be held in the mouth to adaptive keyboards and large trackball mouse devices to speech recognition software. As someone who does a lot of typing throughout the day, I would find it particularly challenging to try to interact with a computer system sans the ability to type. Voice recognition software can come to the rescue, but that's also provided that you have a clear enough speaking voice to be able to control the software to respond correctly and effectively.
Have we noticed a trend in these past few posts? In all of them, I could make some specific recommendations, but there's one that stands out as near universal. Systems that are simply designed, with a minimum of clutter, are going to work better for anyone with a significant disability. What's more, a simpler and cleaner design will not just help those with disabilities but will be more helpful to everyone. Also, the last big takeaway from the motor disabilities page is that most devices mimic or interact with a keyboard so we would do well to make our products as keyboard friendly as we can, and in the process, require as few keystrokes as possible to accomplish the tasks we need to.