I like "j".
It's open source, good with arrays, elegant, and so
concise that it can improve programmer
productivity about 10x.
For example, you can write a really small function
to calculate the average of a list of numbers:
$ avg=: +/ % #
Run it with
$ avg 1 2 3 4
2.5
It's like apl with a normal keyboard.
http://en.wikipedia.org/wiki/J_%28programming_language%29
Thanks,
Kingsley