The Scheme programming language. As close to the core essence of programming as an actually usable, practical programming language has ever come.
LLVM. Being able to fully represent general code in a simple, well-defined, readable text-based format is a far bigger achievement than you would think until you look at what it took to do it.
I think he means R5RS. But honestly, It's missing a bit of what you need for most programming. Chicken Scheme is probably the best actual scheme on the sliding scale of elegance/power, IMHO.
LLVM. Being able to fully represent general code in a simple, well-defined, readable text-based format is a far bigger achievement than you would think until you look at what it took to do it.