[jetti]

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.

[zerr]

> you are going to be paying for Dyalog

Not really. As I see APL is ISO standardized and there are many implementations.

[jetti]

There are many implementations but not as many that are active (here is a brief list https://en.wikipedia.org/wiki/APL_(programming_language)#Mod...). Dyalog provides more than just a interpreter/compiler but an entire development environment.