[liveranga]

J is definitely more batteries-included than the open source K implementations.

There's also a wealth of documentation and books on J: J for C Programmers: https://www.jsoftware.com/help/jforc/contents.htm

Learning J: https://www.jsoftware.com/help/learning/contents.htm

And the New Vocabulary "Nuvoc" on the wiki: https://code.jsoftware.com/wiki/NuVoc

Edit: spelling.

[maximus-decimus]

J is also way harder to learn in my opinion due to it having many times more operators. K2 and Q also have official books.