Disclaimer: I haven't tried Nu yet, just read the FAQs. Nu isn't about Ruby semantics, it's about Cocoa and Objective-C semantics. It's a Lispy/scripting way of interacting with the Mac OS programming paradigm. The author is also the author of the RubyObjc bridge, and Nu was a result of his frustrations with the "impedance mismatch" between Ruby objects and code and Objective C.