I'm using Racket right now to develop a machine learning algorithm. The new math and plot libraries are absolutely fantastic. For the brave or foolhardy it makes a viable alternative to R, NumPy, or Julia. (I haven't used Julia. I have found NumPy impossible to install. I want to punch something every time I use the steaming mess that is R.) Racket is far more a real language than the alternatives in this space but it lacks their wide range of numeric libraries.

Racket is also a really interesting language to learn. Nothing else does meta-programming like Racket, or mixes typed and untyped languages (see Typed Racket). However the most fun I've had with Racket is writing machine code directly into memory and executing it straight from Racket.