APPS
My apps relate mainly to education. Typically practice or drill apps.
The cheapest ones are single page entities, originally developed using Adobe Flash so that they could be freely used in class, as a fill-in activity.
The likes of 'mathstrainers pro' has a lot of functionality built in with professional tuition of children in mind.
My best sellers are: piano chords (reference), piano blues (practice) and of my maths-related ones probably Logarithm Trainer.
I have also tried entering the social media arena with pixwap (useful for sharing pictures quickly and easily).
Although I'm a qualified maths teacher my main experience is in Software Engineering which allows me to create well-tested and well thought out apps.