[F22Rapture]

It runs whatever language you deploy to it. .rxe is the extension for the Mindstorms variant of Labview, which isn't necessarily dependent on the platform it's running on. Java for example compiles to bytecode (which I think, though I'm not sure, has a .class extension) which can run on pretty much any hardware for which a Java VM is available and supports the functions of the program.

An example of an extension that *is* platform dependent would be .exe, which is only understood by Microsoft Windows, unless you were using something like Linux + WINE to run them.

TL;DR there is no "extension for the cRIO," it's going to depend on which language you're using.