APL versus A versus J versus K?

Question

The array-language landscape, while fascinating, is confusing to no end. Is there a reason to pick one of J or K or APL or A? None of these options seem to be open-sourced --

Answer 1

To add some more information...

There is an open source version of K called Kona https://github.com/kevinlawler/kona

For q/kdb+, there is a trial version. http://kx.com/download/

The main limitations are 2 hour timeout, 32 bit memory, 3 month license expiration, and the license itself. These shouldn't be too bothersome if you just want to play around and learn something.

Personally, I found q to be the most user friendly since KX translated the monadic (single argument) verbs from K into English words and there is a good amount of documentation @ http://code.kx.com. In addition, the database system is extremely well thought out and flexible.