[mr_dbr]

http://www.macruby.org/ not sure if it's rewritten in ObjC or just integrated-with

[cpr]

My impression is that it's mostly C and some Ruby, plus C++ for the parts that utilize LLVM.

When you're implementing something at the same level as Objective-C, you can't generally use Obj-C itself.

(Witness the Obj-C runtime, which is mostly C and a tiny bit of assembler.)