I have three months to learn 'REXX'!? What the hell is it???

Okay I know it sounds stupid and no, it is not a dog or even a very large angry dinosaur.
But what i have been assured it IS! is an old programming language, perhaps C for for old unix hacks maybe. What I want to know is does anyone know of any good resources, sites books and other related paraphenalia up to and possibly even including where I can possibly get myself this particular compiler.