Scheme - prioritized a 1:1 between syntax and the AST. Reshuffle the syntax, remove the explicit type system.
APL - prioritized arrays.
Haskell - prioritized FP. Also introduced primitives to make things possible with FP that you could do with OOP already (Monads etc).
Smalltalk - prioritized OOP.
Go - prioritized Concurrency.
Forth - prioritized Stack based.
Prolog - prioritized Stack based.
Really isn't that much insightful difference between these languages as you'd think. Not taking away from their history, but you gain nothing from learning them.
And with APL, you leave it the not-so insignificant ability to use any character one wishes, which is again very different from most programming languages (whether one prefers it or not). It's not insignificant that an APL program looks nothing like a program in most mainstream programming languages.
J used to be the only freely available, and with better documentation -- however, it is also a larger language. It seems that recently the K dialects (oK, klong, kuc, kerf, xxl) are plentiful, freely available and well documented.
It is also my experience that K is less frightening to most people - J uses e.g. curly braces independently as operators, which looks a-priori broken to most people (rather than just unintelligible like K does).
And I say "rich" data since other languages are pretty data-centric (scheme of course), but not any that prioritize immutable hash maps, sets, vectors, linked-lists, etc.
you're missing out