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

ELI is a newly developed, freely available, cross-platform, array programming language. Similar to J and k it relies on the ASCII character set. It implements some of the features that (as I know) were unique to k/q/kdb+ such as temporal datatype and inbuilt SQL subset.