I’ve written a few pieces of software and two of them have been somewhat successful, many many more have not.
I once wrote some software for myself to automagically create classroom seating charts based on student relationships.
Turned out a few other teachers also wanted to do this so I gave it a name (Termites) and sold a few 100 licences. I lost interest after a few years and closed down the business but it was fun and profitable for a while.
I also wrote a testing platform for schools and universities with Mitch O’Toole called Think Literacy.
It has long since outgrown it’s name though and is now used for numeracy tests, cloze tests, corporate staff competency, and general multiple choice tests. With all those optionally linked with surveys to uncover relationships.
It has been used in 22 institutions by around 13,000 students.