Is J [0] one of those that gets lots of use? I have tried it a few times, and was impressed by its power [1] and compactness, but its rather cryptic syntax [2] put me off from going deeper into it. Might still try it more some day.

[0] http://jsoftware.com/

[1] It has some superb demos (which come with the basic install) of many kinds of apps, including up to the level of things like OpenGL graphics ones.

[2] Its succinctness [3] may be a virtue, though, once you get used to it, since programs in it are much smaller than in other languages (I'm guessing both due to its APL heritage and due to using a lot of symbols instead of words - based on what little I have read about it).

[3] That reminds me of PG's essay, Succinctness is Power:

http://www.paulgraham.com/power.html