I used it for a telecomms control and billing application I wrote on Amiga. If I remember correctly, I wrote the entire first version of the application in ARexx because the database we were using only had a ARexx API. I remember it having a GUI and everything. It even communicated with serial devices. I then rewrote most of the application in C++, as it needed a better GUI, and C++ made sense for that. The DB interfacing remained in ARexx so there were plenty of ARexx to maintain. A lot of the business logic existed in ARexx.