Dear Bernard,
I use GNU APL under LinuxMint 64 bit. I was an APL programmer in 1980 using IBM APL, Harris APL, TSR APL, PotraAPL, APL 68000, and a couple of others I don't remember. The latest released version of GNU APL operates utterly consistent and natural with all of those other systems in my opinion. I've found GNU APL to be quite reliable, and any bugs found have been often fixed with 24 hours. When you add full source code, APL2 capabilities, along with a component file system and keyed file system, I think GNU APL may be the best system out there!
I am happy to assist you in getting the system up and running on your machine (no charge). If you are interested, contact me privately and we can arrange a time to get this done.
Best,
Blake