I was looking into similar areas a while ago, and I can't say i had much luck coming up with autism specific apps for my son, although they obviously exist:
I defaulted to simple developmental apps for children, aimed at a slightly younger age level for my son, and that seemed to work ok (the hungry caterpillar was a favourite).
On a more general level, you might explore this course:
It's a free online course with excellent resources from the University of Birmingham. I'm just about to start it again (i got a week in before work intervened last time), but I'm confident this would be a great jumping off point if you were to try it.
It seems obvious - given the affinity children have for screens and the very serious effects indiscriminate use can create - that this would be a very hot topic, now and going forward.
