I would like to recommend a behavioral tracker for conditions like: Attention Deficit Hyperactivity Disorder, Asperger's Syndrome, Autism Spectrum Disorder, and Executive Dysfunction.
It could track symptoms like: good/bad behavior, excessive daydreaming, hyperfocusing, perseveration, hyperactivity, sensory seeking behavior (rocking, banging, jumping, flapping, spinning, etc.), low concentration, low motivation, social awkwardness, communication difficulty, sensory overload, anxiety, irritation, stress, excitement, sound sensitivity, etc.
The tracker might also be useful as a checklist for people with executive dysfunction. The checklist could include food shopping, paying bills, cleaning, taking medication, brushing teeth, locking doors, etc.
Also, I know these have already been suggested, but trackers for seizures and digestive problems like Gastroparesis would be helpful as well.