I previously read that karate kata helped a group of autistic people with their stimming problems.
I thought about this, and then thought that people who have problems with stimming should consider
learning tai chi.
As tai chi is known to not only train the motor skills but can also be used to lower stress through increased
oxygen intake (especially from nature early in the morning) but also lower stress levels due to being fairly
strenuous exercise (if you do the stances properly).
It is also an activity that people can do on their own once they have learnt the main sequence of moves (form / kata)
Well worth considering for people out there with problems with stimming.
You may even be able to learn by watching an instructional DVD if you are not comfortable with learning in a group of people.