I'm still trying to figure out the APL language family. I'd love to implement one, eventually, but it's a ways off. (I've done a toy interpreter already, but that was just to make sense of some basics.)
http://www.youtube.com/watch?v=a9xAKttWgP4
Terse, cryptic, powerful. It's like doing magic tricks with code. (Not that that's a recipe for maintainable software, but that's an entirely different debate.)
There's also (meant to mention this before) A+, which is GPL, I believe:
I've read most of _J for C Programmers_, and, this week, I also got _APL: An Interactive Approach_. The mindset is starting to make a lot of sense. (I've also looked at A+, but I'd rather stick to the ASCII variants.)
$mode ascii
Having read more about APL, though, I'm feeling less inclined to write off the extended character setup. Still, it's an issue one needs to sort out upfront. I guess it's the APL equivalent of bitching about parenthesis, when either is a shallow detail compared to what's really novel about the languages.
Many languages seem to have shibboleth complaints, to show when people haven't made it past the surface - Lua indexes from 1, Lisp has the parens, Python has the whitespace, etc. Maybe there's a community value in that, I don't know.