Dyalog is an APL vendor, they also offer a non-commercial license and high quality documentation. They have a case study of a school management system that is a record keeping system [0].
[0] https://www.dyalog.com/case-studies/education.htm
There is a GNU implementation of APL (https://www.gnu.org/software/apl/). Not sure if it is used in commercial applications or not. I would imagine that if you are doing commercial work with APL you are going to be paying for Dyalog.